How to keep a hairstyle overnight?

So, I curl my hair at night and put it in buns while I'm asleep to keep the curls. But my problem is when I wake up part of my hair becomes frizzy, probably from me tossing & turning & sort of rubbing my head across the pillow or whatever. But the frizzies don't really just brush down, so what can I do to prevent or control them? Thanks!