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 :
Gorilla 2 x 2 8mm Interlocking Rubber Tile - Gray - PACK OF 12 – The Treadmill Factory
Gym Flooring: Tiles vs Rolls - 360 Fitness Superstore Blog
Home Gym Rubber Flooring | Perfect Surfaces
Synergee Foam & Rubber Flooring | Synergee Fitness USA
Pro Series Rubber Gym Flooring Mats - Goliath Products Canada
Korea/Singapore Size 50x50x2cm Eco-friendly Soundproof Rubber Flooring Mat for Gym For Treadmill Power Zone Barbell Floor Mat - AliExpress