Well, Rubik has already thrown down a lot of good advice and also pointed out there aren't a lot of buffs that you can share as a psion. As your minion is a cohort, I imagine s/he will be two levels behind you or more. I'd almost suggest intellect fortress and tower of iron will but the second is expensive, weak, and possibly higher level than you have access to at the moment. By the way, what level are we talking here?

I always like elans. They are a solid choice but generally weaker than a human's bonus feat and skill points. Kalashtar are good. They've got some decent substitution features for psion out of Races of Eberron, as do Changelings (but that's for egoists). Consider the Mind's Eye Articles. They are official and have some fun features and prcs, especially the Expanded Classes stuff.

As horribly, horribly broken as it is, I'd almost suggest a Spell-to-Power Erudite. It can translate arcane spells into psionic powers, and erudite can have as many powers as he needs, though you can manifest only a few specific powers per day. This makes a good back up dancer. Figure out some way to keep her/him relatively safe, wait, and then bust out with whatever power you Really Need Right Now.

If you can manage a recharge method for out of combat (like earth spell + earth power + bestow power + torc of power preservation... there are others but tend to be higher level), your cohort can be somewhat of a psionic cleric. Out of combat, he absorbs everyone's pain (empathic transfer) and heals himself (body adjustment + body purification). Until you have a recharge method, it cost too much to be effective. Once you do, it's nifty, and frees up the caster types to focus on something else.

I'd REALLY suggest society mind/vitalist, but since that's either homebrew or third party depending on how you look at it, it sadly doesn't meet your requirements.