Great question. As a parent of two I know just where you are coming from. On the one hand the savings of sharing a room and the other of being stuck in that same room after the kids get to bed!
Well, the good news is that the Disney resorts offer a variety of resort accommodations to allow you the ability to choose the extra room to have the space to escape while they sleep. A great place to start is
Walt Disney World Resort Accommodations. Here you can look over all the wonderful and different on site properties and find the accommodations that fit your families needs. I'm a big fan of
Disney's BoardWalk Inn myself. Those views are so pretty. Remember, this trip is for you also, so take the opportunity to find the resort that allows you the necessary space to relax after a magical day in the parks.
My wife and I have made it a practice to get that extra space in order to enhance our vacation experience. Many of those balconies provide the perfect place for you to sit back, relax and take in the view.
I hope this response provided you with some insight on how to make this trip even more wonderful.