I'm using Eco Earth right now. Working pretty good. The snakes seem to like to dig a crater on top of their flexwatt and just curl up and sleep on it after dinner. Then they kind of just dig little tracks and lay in them lol. I've used ReptiChips too which is good as well but my boas started digging their butts under the stuff and hiding poops and pisses which made it a pain. Also hard to find pisses from the retic. Used aspen for years and it worked but harder to keep humidity. My advice is try different stuff until you find one that works for you. With an AP cage, pretty much anything will hold humidity. I sit around 80-85% humidity with Eco earth. I let it dry out for the most part, then let the snake run around the couch or bed while I push the substrate into a pile and pour some water on it and stir it up, then spread it back out. Usually only have to do that once a month since I throw the stuff out every month for the retic and every 1-1.5 months for the boas.
I hate newspaper personally. It doesn't give snakes any grip. Imagine walking across a hardwood floor 24/7 in socks. It would get old fast lol. But anyways, try cypress mulch, Eco Earth, ReptiChips and see what you like the best. Can also do what I do a lot of them time and switch it up every few orders lol. The snakes really don't seem to care as long as dinner is coming haha. My snakes are pretty oblivious to most stuff. They have grown very complacent. Bet they would die in the wild haha.