4 month old rolls over to sleep on stomach in middle of night.

Went to pediatrician today for 4 month check up told dr my son rolls on to stomach to sleep. Told me not good as 3 of her patients 3 babies have died from sleeping on stomach. Now I am so worried to go to sleep if he is going to flip. Any tips on how to keep him on his back through the night safely? Thanks ugh… should I put him instead of pack n play by my bed where he flips on stomach should I put him in dock a tot in my bed…? Sometimes now he does this hyper extension of his head and scoots down in it while sleeping… don’t know anymore just want him safe