sleeping on belly

My LO is almost 4 months old.. He's recently transitioned to his crib (was a tough week then it just clicked for him!) he's been going 8-9 hours the past few nights.. Which would be amazing if I could just RELAX and go to sleep!!! I literally stare at the monitor & check on him all night. To top it off he started rolling onto his belly.. He seems to be so comfy this way! But I'm a nervous wreck. Any advice for this FTM with this big transition of going into his crib!!  I secretly wish he could sleep right next to me 😔