I just wanted to thank everyone for the great suggestions.
I tried a tiny amount of grapeseed oil, but it left my hair dirty-looking and icky. I then picked up a small bottle of argan oil, which I'd been eyeing anyway, and I've had decent success with it thus far. Just one pump lightly scrunched into my ends after my leave-in and stylers. Between that and a new haircut and a protein treatment, my waves are perking up.
Thanks so much! You all are very helpful!