I really liked shorty-style PUL wraps before we switched to PUL - Stacinators are the best known (their So Simple wraps) but there are loads of French WAHMs who make much nicer ones
. They usually have quite a high rise and fleece cuffs/waistband... like these:
My other suggestion would be wool soakers, you might find some preloved with a nice high rise or could have them custom-made to his measurements - they might be cooler than wool shorties? Or you could try fleece shorties, maybe a kind that doesn't have an internal soaker (Pumpkin Pants? not sure
) so they aren't too thick/sweaty?