Aerial Drain saved my ass many a times, also try buffing up your vit so you dont take so much damage, and if all else fails look at the materia fusion guide on game faqs for a way to make costly punch.

Failing all else, level up some till you get 6 materia slots and 4 accessory slots.

Oh and btw a few people are under the impression that after you get the bangle you hp goes straight to 99,999 - it doesnt.