M.F.
I would stop the 7 pm milk and just give him milk to drink at dinner and nothing afterwards. That might help with the overnight leaks and is a good habit to break as potty-training approaches over the course of this year. I've had really great luck with Pampers Extra Protection diapers (their overnights) and at 37 lbs. your son would wear a size 5. Size 7 diapers seem WAY too big for a child his size. You could also try a regular Pull-Up over a diaper. They make those in much smaller sizes than Goodnights and Underjams. Good luck!