Hi Emily,
Thank you so much for visiting the Disney Parks Moms Panel with your question. My family absolutely loves
Bay Lake Tower at Disney's Contemporary Resort! With your two little ones, the ability to walk to Magic Kingdom Park is going to be wonderful.
I understand your dilemma. It can be difficult to figure out where to have children who are toddler and preschool age sleep while on vacation, especially if they are in transition from a crib to a bed at home. While there are not toddler-size rollaway beds available, I have a couple of thoughts for you on places for your son to sleep.
First, you might consider the sleeper chair in your villa. When this chair folds out, the arms still are a little higher that the mattress itself up near the head of the bed. This is also true for the sleeper sofa. My daughter has slept in either of these since preschool in the Disney Vacation Club villas.
If that will not work for you, when our daughter was even younger, we would travel will a toddler-size air mattress. A child-size sleeping bag would also work. Our daughter would "camp" on the floor of the bedroom, with lots of extra pillows and blankets around her.
I hope that these thoughts are helpful for you, Emily. Have a wonderful time planning your vacation, and please do not hesitate to ask if you have any further questions.