Amazon.com: Foamma 4" x 20" x 22" High Density Upholstery Foam Padding, Thick-Custom Pillow, Chair, and Couch Cushion Replacement Foam, Craft Foam Upholstery Supplies, Foam Pad for Cushions and Seat Repair :
16-in. Square Non-slip Memory Foam Seat Cushions (2 OR 4) - 16 X 16 - Bed Bath & Beyond - 10295231