You can give them a "resting board" made of plywood or sheetrock (plaster board). All my rabbits get a sheetrock board in the center of the wire floor. They will rip the paper off and chew and dig in the plaster, (they LOVE it)... and it is perfectly safe. My Vet is the person that recommended it to me. Keep their hocks from wearing and protects their feet. The limestone base prevents bacteria from growing. I make sure it doesn't cover the corners that they poop in. When there are babies in the cage, I do make sure it reaches under the feeder.
The floor cloth should not have spaces more than 1/2" x 1", with the 1/2" spacing facing up.