My baby turned 3 months old yesterday. For the past few weeks he has been rolling fr his back to his stomach but never did it during the night. Now be has started rolling to his belly during the night and I wake up to find him with his face planted into his mattress. He won't sleep well during the night without being swaddled, so when he rolls over he can't move his arms out from under him to lift his head up and turn it. What can we do to keep him on his back through the night?

Prop firm pillows or rolled up blankets on each side of him.