M.C.
My DD went from her toddler bed (she had a convertible crib...) to a full size. She LOVES it. I like it too, because if she has a nightmare, I can lay with her comfortably in her bed instead of taking her to mine.
My only suggestion is to use slats instead of a box spring. Keep him closer to the ground. :) you can go to any home improvement store, and ask them to cut planks 54 inches. I used 7, and just lay them across the bed frame. The mattress will hold them in place.