M.N.
Is he ready to transition to a regular bed? Maybe if he is in a big boy bed, he might feel more comfortable because he has the freedom to come out for help if he needs it. Does he feel trapped in his crib? It might be an incentive for him to stay in bed if he likes his bed. You could let him pick out the sheets and comforter or even buy a "car" bed off of Craig's List. Just an idea :)