Pillow moss will definitely be safe for your python, but I don't think it's going to have the effect you are looking for.
Pillow moss is a living moss that thrives in humid/damp environments, but doesn't hold humidity the same way that sphagnum moss does.
Once you add the pillow moss and wet it, it will start to grow and then dehydrate again as humidity drops. You'll end up misting the moss to keep humidity up, but in reality your just watering the moss so it will stay alive.
Sphagnum moss acts like more of a sponge to slowly release stored water as humidity over time. Depending on the brands available near you I've seen it advertised as terrarium moss and forest moss. You may also consider looking at your local craft store in the floral section, a lot of people use sphagnum moss in plastic flower arrangements. It also can be found in hardware stores and garden centers, as it is used in actual gardening as well. Just make sure if you aren't buying it at a pet/reptile store, it must be 100% natural sphagnum moss with no added colorings or chemicals.
Once you find sphagnum moss you'll want to rehydrate it. Most of the time I buy it in gently compressed bags/bricks. I'll take the sphagnum moss and put it in a tote and spray it with water. Let it sit for a little while and start to break it up, I'll keep adding water until it is damp/wet and water runs out when I squeeze it. I'll wring the excess water out of the moss and then fluff it up and place it around the enclosure, usually in corners and surrounding the hides. Depending on how dry the air is up there you will probably still need to spray the moss every couple of days, I know I do, but it will keep humidity significantly better than before.
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