I used it by itself at first, only for my winter enclosure. Some of my enclosures I added some wood chips on the top as I have a couple leopards that loves to fill their water bowl with it. The wood chips helps keep it out.
First, are you talking about the long fibered "sphagnum peat moss", or the "sphagnum peat moss" that is more the constancy of coco coir?
I don't like either for substrate. All of my tortoises try to eat the long fibered stuff, and the other stuff was just too messy and stuck to them arose than new coco coir.
I prefer a thick layer of hand packed coco coir for small russian tortoises and fine grade orchid bark works best for adults.