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 :
Traction Premium Rubber Flooring | Costco
Coverguard 3' x 15' XL Garage Floor Rubber Mat | Costco
Coverguard 5' x 7' Garage Floor Rubber Mat | Costco