I reached the stage of the game in which I have access to two familiars and Imbue Familiar with Spell Ability. I want to use this combination to both improve my Action Economy and be able to cast supporting spells (like quickly reaching an ally with Revivify without repositioning myself). And since I'm already using a whole-day-long Polymorph on myself and Share Spells give it to familiar anyway I want to give my familiars some kind of evasive/immune to most things/impossible to target forms. My familiars are not supposed to fight using this new form, they will exclusively cast spells. New form is only meant to supercharge their defenses to untouchable degree, so I don't have to bother protecting them.
Initially I thought about Will'o'Wisp but it could only cast spells with verbal components, somatic components are no-go.
In case it matters: I'm a level 14 dual-progression caster with access to level 6 Sor/Wiz spells and level 7 Clr spells. I also invested in Incantatrix class so my buffs are basically permanent. I also "carry" on myself about 15 different buffs at all times, all of which are shared with my familiars so they are already a bit resilient.
DISCLAIMER: No Wish solutions, no Pun-Pun, no infinite loops allowed.