I would try Lithium - it is not notorious for weight gain. Depakote, Zyprexa, Risperdal are notorious while Lithium might or might not give you weight gain. And, weight gain on Lithium, if it happens, happens gradually, so it you monitor your weight, you can discontinue Li after adding a couple of lbs. With Zyprexa, you may gain 20 lbs in 2 weeks, by contrast.

Akathisia is a major concern with older AP's, but if you take the AP's together with Cogentin, which acts as an antidote for such major neuro side effects as akathisia, you might be quite OK.

I would either try Lithium or an old AP such as Haldol with Cogentin.