I use the vinyl place mats (one in each animal's cage) for a place to lay that is not wire. The wire can be bad for their feet. I had thought to put a couple squares of vinyl floor tiling, but the place mat idea is less expensive and easier to find and replace. It is also a cool place to lay in the summer. My rabbit and ferret love it.
I had ferrets for twelve years. Ferrets should have hammocks and "sleeping bags" to sleep in, in their hammocks. I used to make the sleeping bags from old hand towels. If you don't already have these things, get them! Your ferret will be forever grateful!