Rolling in crib

I know people say by 8 months old it’s okay if your baby rolls in the crib. My baby is almost 9 months old and is starting to roll on his stomach in his crib, he screams when he’s on his stomach. He can roll back but doesn’t for some reason. I’m getting up so much through the night to roll him onto his back again, as soon as I walk out of his room he rolls back onto his stomach. Sometimes when he doesn’t cry and is on his stomach I think I can leave him but then check the baby monitor and he’s face down into the mattress which freaks me out. Sometimes I just take him into my bed in the middle of the night if he keeps crying so I can get some sleep, but I don’t want him to get used to sleeping with me. What can I do? If there is anything I can try with him I’ll do it.