We live in a two-story home (also with a basement that is off-limits to our daughter) and I also suggest a baby monitor. We keep one in my daughter's room so we can hear what she's doing. We had purchased a two-way intercom system (not too expensive from Radio Shack) thinking she would be able to talk back and forth, but it ended up being a little too complicated for her (she would push the button to talk, but forget to hold it in and we couldn't hear what she was saying). So, we put back the baby monitor and use the two-way as a way to talk with her. It has helped us be able to remind her to go to the bathroom or settle down for sleep (she likes to lay in bed to "read" a book before settling down completely). It has also helped at naptime when we've been able to tell she's playing instead of sleeping. :) It's an easy way to talk with her while using the baby monitor to determine if we need to go upstairs.
Remember, too, that this is the age when our little ones will really test their boundaries. Your son may keep getting out of bed just to see how much he can get away with. :) Once he knows the rules at your new home, perhaps he'll settle into the routine you want. Oh! A suggestion I've read before about helping your child stay in bed is to give him cards or something similar as "passes" to get out of bed. Once the last one is used, he has to stay in for the night. Just another thought.