16-in. Square Non-slip Memory Foam Seat Cushions (2 OR 4) - 16 X 16 - Bed Bath & Beyond - 10295231
Amazon.com: FoamRush 4" H x 18" W x 72" L Upholstery Foam Cushion High Density (Chair Cushion Bench Foam for Dinning Chairs, Bench Seat Cushion Replacement, Foam Rubber Padding) : Arts, Crafts