My daughter is in a wheelchair... for her tote bag, I have adapted a 'vera' bag by cutting the straps and attaching parachute clips/buckles to them and turning the straps so they can hook onto the wheelchair push handles.
(! hope this makes sense!!)
You might want to do a google search for wheelchair bags - there are some cool ones out there, for under the seat, and for the side. that kind may be easier for him to reach.
You mentioned a pillow quilt... if he needs a cushion for his back, maybe sewing some loops onto the short end of a pillow to keep it from falling.
I would suggest a gel seat cushion with a lambswool seatcover. His butt is going to be sore from sitting!!
Hope his recovery is speedy!!!