baby bumpers yes or no?

Ever since my little one has turned 3 months he's been able to flip from his back to his tummy! We were very excited at first till this posed a new problem at night .....LO was starting to scoot while in his crib and beginning to bump his head sometimes very hard. He'd obviously get upset And I'd flip him back on his back and put him in the center of his crib but would hear him bump his head minutes later.
So I've heard about bumpers being dangerous, has anyone tried them? Any other suggestions to help LO from continuously hitting head?
Has anyone else had a hard time with LO since they've been able to flip from back to tummy?