Husbandry Troubles.

[WickedViperess]

There's a lot of posts of other people having similar problems, and I've read as much as I can but I'm still struggling.
I got my very first Ball Python yesterday. I love him dearly and want him to feel comfortable.

I've gotten his cage set up and tweaked it as I learned more about husbandry for BPs, before I even bought my snake.
Now that he's here I worry if everything is as he needs/likes.
My set up currently is:
2 Hides, both on your standard cool side, and hot side.
1 water dish, placed in the middle of cage.
some fake vegetation for a natural look and some enrichment.
A "natural" background so the snake can feel a little more secure.
a mix between sphagnum moss and repti-chip substrate.
It is a glass terrarium, Exo-Terra, Large Low (36x18x12), because plastic ones have been a bit far out of my price range.
3 light fixtures, one with a day time bulb(100watt), and night time blub(75watt) to try and keep the ambient temps warm and 1 bulb with uv lighting on the cool side(I know BPs don't need this but I heard they can kind of benefit from them so I gave it a try)
UTH on the hot side, set with a thermostat to keep it from going above 90.
I used the box top the cage came with to cover the screen top, both to try and hold heat in and to keep my cats from walking on top of it potentially hurting themselves and my snake.

Right now my problem is mostly humidity. I live in a pretty cold climate and while the humidity outside can be as high as 80% even in winter, the rooms tend to be kinda dry. I've tried only misting mornings and nights, and they do go up to 50%, however, after a while they still only hover around 40%. I have some holes cut into the cardboard top for the lights and a little bit of ventilation, and a row of holes cut towards the front. (I believe that might be the reason the humidity escapes)
Granted as of right now, my only method of tracking these are with stick ons, which are notorious for being inaccurate. And as of right now, with Covid-19 making a mess of things, trying to buy a digital one online is going to take a month to receive. I could go to walmart and see if they have any there but I don't even know which ones would be good.
I heard "ThermoPro TP49 Indoor Digital Hygrometer/Thermometer" would be nice, looked at the reviews for it and they're all pretty good, but I'd like to take some advice from people who have done this for years.
I also feel my cool side might be too cool, but I have no sure-fire way of knowing. Stick on says 80 but it hasn't moved much for a few days and fear it may even be broken. (Or they're working fine and I just don't know!)
One method I want to give a try is to use some aluminium foil and cover the lights and some of the screen, and just watch closely.
However, any advice will be considered! I feel in love with this little fella and want the best for him.