I know there’s these underwear that have a padding where it won’t leak through and wet the bed but will let them feel that wet sensation so they know they had an accident
Try putting a potty in his room to use. A puppy pad or changing pad can help contain any spills.
If he’s peeing at night in a pull up, he’s going to pee at night in underwear. It’s not gonna make a difference. You can’t night potty train