So I am building a campaign and need some advice on a mechanic for sanity/madness I’m working on. I don’t much like the current ones available.

basically you would calculate sanity points like you would hit points. Except with sanity die instead of hit die.

artificer- d10

barbarian-d6

bard-d10

cleric-d10

druid-d10

fighter-d8

monk-d10

paladin-d8

Ranger-d8

Rogue-d10

sorcerer-d12

Warlock-d10

wizard-d12

the modifier you would use is = (wis mod + Int mod)/2

• any Psychic damage applied to HP is also applied to sanity

• when a pc takes a critical hit, half of that damage is also applied to sanity

• when a pc fails a death saving through by 5 or more, take an amount of sanity equal to 1 sanity die.

• if you’re sanity is reduced to half or less of its maximum, you have a 25% chance to harm yourself if you miss a Mele weapon attack or 25% chance to harm one of your companions on a ranged weapon or spell attack. (If you’re attack or spell misses, roll a d4 and if you get 4, you accidentally hurt yourself or the spell/ranged attack hits one of your party members)

• If your sanity is reduced to 1/4th it’s maximum, you begin to Experience derealization, hallucinations, and other burdens as reality begins to warp all around you. Disadvantage on wisdom (perception), intelligence (investigation), at wisdom (insight)checks and saves.

• if your sanity is reduced to 0, you no longer have the will to live, and have disadvantage on death saving throws.

I like how this works. However i think instead of hurting yourself or others its always one or the other. Flip a coin, heads is yourself, tails is others. At that point id add it so for the last one instead of having disadvantage to death saving throws you become hostile to the party

First, I think Warlocks should have a d6 sanity hp.  Cultists are not particularly sane. 

Second, people should have an ability to heal their sanity.   Whether it is 1 pt per long rest, or something else, it should exist.

I would also grant bards, monks, warlocks, clerics and paladins additional sanity healing in some form.  Monks both for themselves and others. Warlocks just for themselves. Bards, clerics and paladins just for others.

Finally, I think you should have additional options for insanity.  Specifically, most crazy people have major disadvantages to normal life.   So I would have some option of disadvantage on Int, Wisdom and Charisma skills.

I disagree with the sanity die given to the classes,  but that might be more personal preference or beliefs. Why doesn't warlock get the highest at d12? Why would a ranger & paladin have lower sanity than a bard? I don't know the numbers I'm expecting but I know it's different from what's presented. 

i did think about it, however, I felt like it would be taking away my player’s control over their character.