Put a baby monitor in his room so you can hear him if he gets up. Put a baby gate across his doorway that he can't get over. If he is mobile when you are out of sight you must make sure every bathroom door and exit from the home is shut and locked with childproof locks. Kids can tip over into toilets and drown and if he gets a door open he could end up outside.
There isn't any way I'd feel bad about making sure he can't get out of his room, I expect that you do have his furniture secured to the wall so that if he climbs on it he can't topple it over, right? And that if he has any shelves there are L brackets under each shelf so it can't come out and hurt him? No toys for above age 3?
Then his room is safe for him to be in without you hovering. He can wake up, play, lay down in the floor even. If he is safe then it won't hurt for him to be up. A baby monitor will let you hear him if he wakes up.
Make sure he's eating a good snack before bed so that he isn't waking up hungry. We put the kids to be later in the evening and they had a snack before brushing their teeth and going to bed. When they had a good snack they seemed to sleep much better.