Yeah, you really have to budget the hell out of your items. Although, here's a tip for healing yourself easily.

If you choose the "defend" option with a character in battle, that character will get a 50% damage reduction and some percentage of their HP back at no cost. If you're only fighting one enemy, you can just defend like crazy with everyone and within a few rounds, all of your characters will be at max HP. So, if you're low on HP, get into a fight, kill all of the enemies except one, and then choose "defend" with every character, every round until you're at full life.