Feats are a no-go...
I'm not aware of any feats that will do what you want. A couple options that won't work for you:
- Divine Shield (Complete Warrior, p. 106): Healers aren't allowed to use shields. This is dumb, but true. If your DM is willing to relax this restriction, it becomes an OK option, but you still have to spend standard actions activating it, which isn't great.
- Ascetic Mage (Complete Adventurer, p. 105): You have to be a Monk or Ninja first, and spontaneously cast arcane spells.
The best feat option I know of for you would be Combat Panache (Player's Handbook II, p. 93), but it's not great. It requires you to:
- Deal damage to an enemy
- Make an Intimidate check against them as a move action on your next turn
...and even then, you only get the bonus against that enemy (technically they take a penalty to their attacks against you, but same diff). Probably not a great choice for you.
...but you have other options.
If you're willing to consider options other than feats, there are lots of things that could work.
Wisdom:
- Monk 1: The classic way to get your Wis bonus to AC. Straightforward, but costs you a level.
- Ninja 1 (Complete Adventurer, p. 5): See Monk 1, but darker and edgier.
- Swordsage 2 (Tome of Battle, p. 15): Pretty much the same deal as the Monk dip. Costs an extra level, but works with light armor (which the Healer class typically uses), and several Swordsage maneuvers could be useful for your character, especially the Shadow Hand school.
- Monk's Belt: Basically the Monk 1 dip without spending a class level. 13000 gold.
- Saint Template (Book of Exalted Deeds, p. 185): A +2 LA template that gives Wis-to-AC, along with several other excellent bonuses. Generally regarded as one of the stronger templates. Comes with alignment baggage. Check with your DM about both balance concerns and the ridiculousness of BoED content in general before you take this.
Charisma:
- Battle Dancer 1 (Dragon Compendium Vol. 1, p. 26): Works like the Monk dip, but for Charisma.
- Red Falcon 2 Paladin Substitution Level (Champions of Valor, p. 48): Cha-to-AC for one round as an immediate action; replaces Divine Grace. Probably not worth it, but it exists.
- Risen Martyr 2 (Book of Exalted Deeds, p. 68): Charisma bonus as Deflection bonus to AC, always active. All the caveats about BoED apply double for this class. It's stupid and its capstone is you become an NPC. Work with your DM to make it less dumb if you're interested.
Most of the info in this answer was found by scouring the X stat to Y bonus thread, one of the all-time great 3.x optimization resources (along with the Lists of Stuff). If you bookmark anything about 3.x char-op, bookmark these two threads.
