Girls, give me feedback! We've been flipping back and forth from belly…

Girls, give me feedback! We've been flipping back and forth from belly to back for three and a half months. That being said, I haven't slept through the second night - the baby turns over from back to belly in her sleep and doesn't make sense naturally that her head needs to be on her cheek while she sleeps, it presses right into the mattress, you can't do that. How do we fix this? (I'm afraid for her) Maybe there's a life hack for experienced parents, tell me!