If he has mites, I wouldn't bother putting in anything other than paper towels until you get the mite problem corrected. Otherwise you will just be throwing out the bedding as you treat him and you won't be able to see the mites as well.

To keep your humidity up, a bigger surface area water bowl can be used to increase evaporation. Also, cover at least half if not 3/4 of the screen top with plastic wrap and/or aluminum foil. This will help keep the humidity in the tank instead of letting all out of the top.