I got a 6’ roll of 3/4” foam pipe insulation for like $2.75 at Home Depot. Figured if I screwed it up I’d have extra for a redo, I think it came out just fine.
I say use the beach noodle. Much more comfortable! I picked one up at the dollar store and had enough left over to make several more. Just cut to size, add slits for the shoulder straps, paint the ends with acrylic paint, wrap in black tape, secure with zip ties and you’re done.