i would suggest you get a large fleece type bed for the whelp box where the pups are. no loose blankies or towels. i have been able to use loose bedding in the past myself with no problems. neat little mommas....
but my courtney will dig and dig if she has loose bedding in with her babies so i use a flat bed with soft sides for them. i'm attaching a pic to give you an idea of the bed to keep her from flipping them all around under the bedding!
(place your heat pad under the bed between it and the box on 1/2 of the box. turn it sideways if you have to. good luck!