More comfortable….new guy

Hello everyone, 1st time here-just joined. I just bought a 2006 Kodiak 450. Original owner, 1600 miles, winch, plow, excellent shape. Anyway, have/had motorcycles, rode plenty of quads, but this my first one.
Single dad, always with my son. Sold the Harley cuz he’s 7 and can’t ride with him, so I figure going out on the quad is the way to go. Now there’s a Koplin storage box on the rear rack with a small cutout for a passanger, but no cushions. I want him comfortable and not really concerned about having tons of storage. I could go with a front bag/box for that.

Ok— do I go with a hard box with seat like a Tamarack or go with a soft bag with seat? Which would be more comfortable for him? My fender protectors just came in with the foot pegs for him.
Thank you,
Brian….I mean faxman