Which is the best bedding(substrate) for my 5 month old baby ball python?

I used repti bark too. Mine is about 1 1/2 now 3 feet and some inches. Hes does fine, it keeps humidity up to, I also keep him in a bin.

I use regular old paper towel for all my snakes. King snake, corn snakes and ball pythons. Make life easier for clean up. Because of the area I live in, humidity in our air is high enough for snakes until winter so I usually do not have this issue. But during winter I just spray the tank if the humidity gets below 50%. If you do not have the patience for this you can try coconut husk. It holds moisture well, just watch for mold growth and clean out the coconut husk every month and if you see any signs of mold.

I use aspen with my ball. And keep a larger water dish on the cool side of his tank. That solved the humidy problem for me. I have used reptibark bedding before with some good luck on keeping humidity up.