Sounds tricky. Does he have a dummy? We actually put our DS to sleep on his tummy during the day (he won't settle otherwise) and the dummy gives a bit of space between his face and the mattress. It's a hard one. If he has good head control and can lift his head, I wouldn't worry too much. OUr paed said it was ok to let him settle on his tummy now but we have been doing it for awhile so he will go to sleep in the day. Hope you can find a solution.