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 :
Rubber Garage Flooring Buying Guide
SportFloor | Rubber Stall Mat - 4' x 6' x 3/4"
4 ft. x 6 ft. Thick Rubber Stall Mat at Tractor Supply Co.