Use less substrate. There should only be a 2-5* difference between the top of the substrate and the glass.
Your biggest issue is using a 55g tank. That tank is not made for ball pythons, it is made for fish. You will end up heating a lot more air than you need to. Try getting a 30g breeder. That has almost exactly the same footprint but is 12" shorter.
You could also try insulating the sides and back of the tank with dark paper to help hold in heat.
A CHE is basically a lamp without light. It only gives off heat. They are expensive, but they last for a long time. The other catch is that is will drain all of the humidity in the tank. I would personally avoid it since you seem to be having humidity problems already.