Just in case I ever make any of those cool pallet furniture ideas. This is a great site to get those foam mattresses needed for those DIY indoor/outdoor sectionals. They have the best prices I have found.
Upholstery Foam 3" Thick, 24" Wide x 72" Long Medium Density by fabulessfabrics on Etsy https://www.etsy.com/listing/154271906/upholstery-foam-3-thick-24-wide-x-72
DIY Upholstery Supply - this site has tools, materials, supplies fabric + videos, tips a QA board.
Upholstery Foam for sofa Cushions
High Density Foam, Custom Cushions, Upholstery Foam, Cushion Replacement, Mattress Pad
Polyurethane foam Upholstery foam cushion high density standard (seat replacement , upholstery sheet , foam padding) Has a compression rate of 44 lbs and it features the perfect amount of cushioning and stiffness http://acnevideos.com