Hi Pat,
I use interlocking anti-fatigue soft tiles bought at Lowe's or Home Depot, I can't remember which but I think both stores carry them.
Soft tiles are foam, about 1 foot square and the edges fit together so you can make them into whatever size you need.
Mine are about 7 years old and they're still structurally sound and great for my feet and legs.
You can see them here:
http://www.softtiles.com/?gclid=COqh...FQspFQodq2xueg