Girls, what should I do? The baby keeps turning in his sleep. He flips…

Girls, what should I do? The baby keeps turning in his sleep. He flips over on his belly and wakes up. Starts crying. Has anyone experienced this? Only under my side is he sleeping peacefully because I hold him, don't let him turn over completely. Otherwise, as soon as he turns over on his belly, he automatically gets up on all fours and freaks out. I would probably be happy to sleep with her, but I don't get enough rest because he keeps turning. And also, we think our mattress is too soft for this little back.