If you've got the magic mantle, take Sanctified Spell (that's the one that makes them Good-aligned, right?), Words of Creation, item creation cost-reducers, then make yourself a really high-ML psychoactive skin of proteus. Those types and subtype changes can give you a number of immunities (fire, cold, poison, Good/Evil/Lawful/Chaotic spells, mind-affecting, language-based, level drain, ability damage, fear effects, and so on), as well as utility out the wazoo and amazing combat potential.
Don't forget about the tinfoil hat trick.
Feel free to use the hell out of your psicrystal's goodies (non-language-based telepathy, flight, near-blindsense within 40', immunity to starvation and thirst, no need to sleep, etc). And don't forget that with ML boosters, an erudite can learn higher level powers/spells and manifest them when he boosts himself high.