Hey all, been a while, Covid, 70 hour work weeks, yada yada.

Long story short, I want to make the monk class a little bit more user-friendly and beefier to keep it competitive with the other classes, and I could use some feedback.

1) Ki Points: I am planning on adding the player's Proficiency Bonus to this pool. Yes, at higher levels, this is likely to lead to an insane pool for the player, but at the same point, if you aren't Kung Fu Fighting the BBEG square in the taint, then what's the point? I am also planning on, as a full-round action (Taking both attack and movement actions) the player can reach deep and fully recover their full Ki Point Pool, but doing so will do 1D4 damage to their hitpoints for every Ki Point recovered this way, since they're pushing themselves beyond their limit, and this damage is not resistable or negatable in any way since they're doing it to themselves. Otherwise, Ki Points remain as close to R.A.W. as I can. Thinking of limiting the 'Reach Deep' part of the ability to once per Long Rest for balance reasons.

2) The M.A.D. Issue: I am planning on two 'Foundational' Schools on which all the others branched off from. The Perfect Body and the Enlightened Mind. Perfect Body replaces the Wisdom part of the Monk's Unarmored Defence class ability with their Constitution score instead, as well as their Ki DCs for Stunning Strike and the like. Enlightened Mind, however, retains the Wisdom component but reduces the cost of recovering your Ki Poins mid-battle to just your attack action, and reduces the damage to 1D4-1, possibly negating the damage entirely. Tying these to the 'Internal' and 'External' martial arts. So if you want to be a beefy front-liner or the brash action hero, go for the Perfect Body. If you want to be able to spam Ki Points like you're a MC from Naruto, or be the wise and preternaturally focused martial artist, choose the Enlightened Mind instead.

3) Patient Defence: Can be used a number of times equal to your Proficiency Bonus, after which point it requires a Ki Point to activate. Resets after a Short Rest. (leaning towards Long Rest for the reset to avoid becoming broken)

4) Step of the Wind: Can be used a number of times equal to your Proficiency Bonus, after which point it requires a Ki Point to activate. Resets after a Short Rest. (leaning towards Long Rest for the reset to avoid becoming broken)

5) Stillness of Mind: The Monk has advantage on saves required to realise they've been charmed in addition to the rules as written for this ability. Intelligence for realising this isn't a smart move, Wisdom for this being unnatural, Charisma for it breaking their moral and ethical codes, etc etc.

6) Perfect Self and Timeless Body: The Monk's Timeless Body is enhanced by Perfect Self, rendering the Monk functionally ageless so long as they have one Ki Point left. While in this state, they remain at their physical and mental prime and cannot be aged artificially or magically. If they expend all their Ki Points and do not recover them from a Short Rest before the end of the day, they will begin to age again and, depending upon how old they really are, may age to death in their sleep. When they have no Ki and roll for initiative, they regain half of their Ki Pool, not just four piddly points.

Any feedback would be appreciated as I've only been DMing in 5th edition for about four years and I think I've seen ... three monks in that time, and none that were played beyond 7th level before the players retired them for something else to play or retrained to another class.

Patient Defense I would make per long rest. It’s a powerful ability. 

No need to do damage on the recovery of Ki points, just make it a once per long rest 1 minute of meditation out of combat I think would work fine. Or just give the party more short rests. 

How about making the “proficiency bonus Ki pool’ rest after a long rest and leave it at that?

Also give him the "mobile" talent. This feat saves a lot of ki points and makes the monk an easier character to use.

If he lacks defense there is the Ring of Protection and Bracers of Defense.

If he lacks damage you invent him a Martial Arts book that allows him to use the defense bracelets as weapons, and this add the +2 defense to the damage.

I don't really have much to add on the specific suggestions that hasn't already been well covered. Although as I've pointed out on other threads Rogues getting Cunning Action for free isn't a good justification for Step of the Wind being free (From 2nd-level Monks are nearly as fast with a single dash as the Rogue is with two, so they're not actually the same feature really); being able to Dash for free as a bonus action does still trade damage (from Martial Arts/Flurry of Blows) though so that's fine as a trade, but free cost double dashing may be too much if your campaign uses distance/speed a lot.

What I would say is that it sounds like you may be doing this prematurely; three Monks in four years is anecdotal, you don't know what difficulties this particular player may or may not encounter, or if they'll encounter any at all (they may be happy with the challenge). If you're looking to "fix" the class so that they have the best experience then the best thing to do is tailor any house-rules/homebrew to the difficulties they're actually having, rather than trying to solve everything in advance.

As Aanx points to there are also existing tools you can hand out that can quickly rebalance the party without requiring any custom rules at all.

Also, their experience is heavily dependent upon the campaign and party. For example, if the party already has a Barbarian, Fighter, control Wizard and a Rogue, then this means the Monk's toolset becomes pretty redundant, but that on its own isn't a problem as with sufficient challenge a bit of redundancy isn't a bad thing, as if you're facing multiple enemy casters that need taking out quickly then one Rogue isn't enough, even two hyper-optimised front-liners can need a third set of (flurrying or blocking) hands and so-on. This is true with most characters.

So yeah, personally I think low level Monk is fine as-is; you should wait to see what, if any, difficulties the player actually runs into, encourage them to talk to you about anything they feel is lacking, and respond to that directly. Which really is true of all classes.

Not that it will hurt to have some ideas in the bag for various features just in case, but I just want to make sure you're not losing focus trying to fix everything in advance. 😉

I'd like to thank you all for wading into this hot mess of a thread with me.

On the point:

1) Ki Points I think I'll add the Proficiency Bonus to their Ki Pool, but give them a 'once per long rest' recharge mechanic to get half their Ki Pool back, but after combat it gives them 1 point of Exhaustion. At lower levels, this might lead to a strategic moment that lets the Monk pull off some crazy stuff with a heckin' problem that they'll have to deal with until their next Long Rest, and at Medium and High Levels, probably won't matter all that much considering what the rest of the party can pull off. While the d4 hit-point loss would have made it more tactical, the Monk is already struggling for hit-points and while it would have been dramatic for the Monk to tear themselves up to get enough Ki back to finish the fight, the possibility of the Monk K.O.ing themselves right when their party needs them the most is quite high.

2) The M.A.D. Issue: You're right, this added little and just muddied the water for a Class that's already trying to do fifteen different things at once with three stats.

3) Patient Defence: Definitely a Long Rest thing. Did some rough solo-testing and that's a big yikes to have it as a Short Rest recharge ability.

4) Step of the Wind and 5) Stillness of Mind: I'm gonna leave these in as Short Rest Recharge abilities. I was sorely tempted to build in the Mobility feat, but I think I'm Frankensteining the Monk too much here and might make it too stronk.

The final two abilities I'm gonna leave in as flavour more than anything else, ie old martial artist in the mountains, guru of a thousand students, sage living humbly amongst the poor and providing healing and teaching to the downtrodden, etc etc, have it as the capstone for why some pursue the path of the Monk, for the eternal life, while others reach the goal after a lifetime of pursuing internal alchemy, or following divine teachings and bringing their body into harmony with these teachings.

Once again, thank you all for stepping in and offering some damn good advice and critique.

Another thing you have to be careful with the monk and his many features that are practically unused, because these are very situational and so it is up to the master to create the situation so that they can be used. This is not only true for the monk but for all classes that have powers that are not always so much used. So create a story based on the different abilities of the characters so that each of the players can be part of the adventure you are creating. I say this because it is sad to have so many powers but never use them.

I've always rolled with a more 'rule of kool/you are the badass' rule with D&D and let classes/characters that have an unused reaction and the ability to block, deflect or catch missiles or other ranged attacks to declare their reaction as to block, deflect or catch said missile or magical effect, if it makes sense and is logical for them to do so.

Characters with the Protection or Interception fighting styles, Monk's with their amazing quirky abilities, etc etc. Letting your players do things on the fly that might straddle the line of the rules is, to me, what makes a game fun, but I'm also lucky enough to have been a part of a team of players and DMs that accept that the DM does have final say on if a thing will work if it falls outside of the R.A.W. or R.A.I.

I am looking to give monks a d10 HP like any other martial character.  The argument "But they're skirmishers" doesn't convince me that they should start with less HP potential just because the are supposed to be mobile.  Barbarians are mobile, and they get a d12; Rangers are skirmishers, and they get a d10. And rangers get armor, as well as barbarians tho it negates their unarmored defense. Just that small change would help the class imho.