Thanks for the additional details. Er, apologies if I just missed this info elsewhere in the thread, but is your heat lamp the only thing that is regulated by the thermostat? The UTH needs to be regulated by a thermostat as well; any heating appliance has the potential to overheat, and that's the main thing you'll want to prevent, for your snake's safety.
I am glad that you moved the tank away from the windows, both to remove the contributor to a temperature inconsistency, and because it may also have been too bright for your ball python.
Humidity, hmmm! Misting more frequently may help. I've heard that coconut fiber substrates such as Reptile Prime are effective at holding humidity. Some people add little clumps of dampened sphagnum moss or terrarium moss throughout the tank.
I like a splash of color in my enclosures (though I use Sterilite tubs), so here's something I've found to be a good little "humidifier." I have some little dense-leaved plastic plants as decor that were originally intended to be aquarium accessories. When I want to bump up the humidity a notch, I run the plants under the faucet until evenly wetted, gently shake off the large excess droplets, and put them back in the enclosure. Because those leafy plants have a lot of surface area and nooks and crannies, they seem to hold a good amount of water in them that then gradually dissipates into the enclosure.
Something like this: https://www.amazon.com/ByTheBay-Plas...gateway&sr=8-2