So I've looked at countless posts and suggestions, but I still find myself stuck in analysis paralysis for my level 12 feat selection. I'm playing a variant human shadow sorcerer with a wide range of control and debuff spells. The party has a cleric, but otherwise I'm the only full caster. Cha is maxed, all other stats are even (10, 12, 16, 12, 14, 20), took metamagic adept already. Party paladin took Inspiring Leader, so that's off the table. Here are my ideas, let me know your thoughts:

Alert: +5 to initiative allows me to get in my control spells before melee folks are engaged. Sure, makes sense.

Fey Touched: More spells, with misty step being the selling point. But I can't shake the feeling that this is a waste since I'll get Umbral Step at level 14 anyways. If I took it though, I'd probably go for Resilience (Wis) at level 16 to really boost those wisdom saving throws.

Martial Adept: I sense your judgement, but hear me out. I have a homebrewed dagger that essentially functions as Shadow Blade, but without requiring concentration. So a thrown finesse weapon that I use my spell attack to hit with that does 1d4+2 piercing and an additional 2d8 psychic on a hit. My thought was I could add Quick Toss (use dagger as a bonus action and add a d6 to damage) and then either Commander's Strike (give somebody else an extra attack while I'm maintaining concentration) or Rally (bonus action temp hit point boost that's Cha based). Downside is obviously only one use of one ability per short rest.

War Caster: Obviously in play especially with the amount of control spells I utilize, but I already have +7 to my Con saves and advantage is good but it also doesn't feel super necessary? Although I'd probably start twinning haste like crazy if I picked it up.

I've also considered but largely ruled out Shadow Touched, Ritual Caster, and Magic Initiate since most of those areas are covered by our cleric or some of our half casters. And I don't really want Lucky.

Here's an idea, if you can take it: Aberrant Dragonmark (Shield).  You get:

• +1 Con, and you can take another +1 Con half-feat at 16.
• You learn a Sorcerer cantrip.
• You learn Shield (if you already know it, just replace it, so you end up learning +1 level 1 spell).  Your AC is hot garbage, so this could be clutch.
• You can cast Shield 1/short rest without using a slot.
  • When you do this, you can roll 1d6; on a 2, 4, or 6 you gain that many THP.  On a 1, 3, or 5, a rando within 30 feet of you takes that much force damage.  Optional effect.
• If your DM is willing, you have a 19% chance to gain a boon.

Trick above works with any L1 sorcerer spell, but it's best on something you want to cast an extra 3/day without upcasting.

Other than that, the only options I'd add to your list are +2 Dexterity, since your AC is atrocious, and Eldritch Adept (Devil's Sight) - you can already see through your own Darkness spell, but other than that, you need to consume a spell known and an L2 spell slot to have mere Darkvision - Devil's Sight is a good deal better.

Personally, I would take telekinetic just for the additional battlefield control

Shadow-Touched.

Free invisibility, free 1st level choice - I tend to go with Inflict Wounds.

Mind Sliver + Hound of Ill Omen + Hold Person = enemy lock down. And you get to then walk up to the enemy and cast Inflict Wounds at highest level which is with advantage (and there's Seeking Spell Metamagic) and autocrit for a not too shaby 16d10 necro damage. And if the hold spell, well, holds: your next highest at 14d10 necro damage.. and so on. Big Bad, feeling free with sorc points - oh so this inflicting of wounds is a quicken spell bonus action and your continued mind slivers are your actions. Excellent. Cleric in the party? Oh, a nice free bane.

Good luck big bad. Disadvantage, -2d4, to the saving throw - yeah they're pretty much stuck as you unload torrent after torrent of auto-critting inflict wounds. 

Even if the Cleric has inflict wounds too: so what? that just means you'll get the bad guy dead right quick and hey, maybe you Twinned that Hold person so both you and the cleric have your own targets?

Or maybe just take it for the free dark-themed spells like Invisibility and Silent Image or Disguise Self. Or show them their horrors with Cause Fear. Shadowporting around invisibily is a great way to get your dark-soul groove on.

I mean, you're a sorc. You need the spells. Even fey touched still good choice. Sure the misty step is overshadowed by the whole shadowporting thing but listen: you're probably not going to be in dim light or darkness 24/7 now are you, so Misty Step remains useful. As will that extra 1st level. 

Get them both. That'll be 4 more spells known (and by crikey do you need more spells known), 4 free spellcastings per day, and you might make some choices you normally wouldn't get as a Sorc. These feats are a sorcerer's dream. 

If you want the strongest feat in the game and your DM allows it, take Lucky.

I'm currently in a very similar situation and am planning to take Ritual Caster at level 12. Only other full caster in my party is also a Cleric, which leaves all the Wizard Ritual spells unavailable to our party. I know you said you ruled it out, but Wizards have some really good rituals that Clerics don't have access to.

I think War Caster is best, because you'll be taking more than 20 damage at once fairly often now that you're a higher level character.  Also, being able to cast a spell as an opportunity attack can be fantastic, especially since it doesn't have to be a cantrip and it can be a debuff (like Tasha's Mind Whip) or Hold Person.

Another option is Skill Expert & Resilient Wisdom as your level 12 and level 16 feats.  If you're the party face, Skill Expert could be useful.