If your son also likes quilts, you could make a comforter (duvet) cover. Piece the top as you like, add a back and use a zipper or buttons to hold any comforter or feather tick inside. I put bias tape in the upper corners of my comforter covers and on my comforter so it doesn't shift around. Looks like a super fluffy quilt.
Good luck and happy quilting.

My son doesn't own any comfortors just quilts. He use to have a twin size bed and now it's a queen. I'm just going to jump in and hope for the best!