Costco (in Canada at least) has these sweet rubber mats that remind me of the gym. Way cheaper than Amazon since they are heavy as heck! It's flat on the other side :
Survivor SportFloor Isometric Grey 48 in. x 180 in. x 0.3 in. Rubber Gym/Weight Room Flooring Rolls (60 sq. ft.) 01050805082 - The Home Depot