My dogs have always preferred the dense cotton round cushions from papasan chairs. The ones that are 4-5ft across work great. I recently cut up a memory foam single mattress from craigslist to fit some covers I found on Amazon. Inner liner is water proof, outer shell is water resistant, washable, easy to put on, and holding up fine under big paws. https://www.amazon.com/gp/product/B0075QAYP8