Belly sleeping

So we’ve been trying to get baby crib trained, but he will only sleep in there on his stomach. I refuse to put him down on his stomach, so he ends up back in his bassinet after 30 min sleeping in his crib. Of course, I know they say if they flip themselves over to their stomach just leave them. Which is what I was waiting for. Well, last night he immediately flipped to his stomach when I laid him down, and after about 2 hours I noticed he was laying face down with his face buried in the mattress. Soooo I flipped him over, he woke up, and wouldn’t go back to sleep. Anyone else’s baby sleep like this? Should I just leave him alone? He will be 8 months on the 14, and the bassinet is getting less and less safe every day.