So I recently adopted my first ever snake, and I am very excited about it. I did tons of research into proper care and husbandry but I'm still a little unsure about my heating system. I live in the Pacific Northwest, and I am a college student so my house is generally unheated and rather cold (think about 65*F). I am housing my ball python, Pixie, in a 10 gallon glass terrarium with a locking lid as she is only about 70g. I covered the back and side walls with construction paper to make it a little less open.

During the day I have a 75watt UVA/UVB light which I mainly use to maintain a day/night cycle with a light timer. For heating, I have an ExoTerra 10-20 gallon heat mat underneath the bottom on one side of the tank (on the outside, using the peg feet for proper ventilation) and I have the thermostat probe on the glass on the inside (I secured it using aquarium silicone) which I keep set at 90*F. Because I was a little worried about the ambient temperature I got a Zoo Med Mini UTH which I put on the side wall (on the same side as the other heating mat) and because there isn't substrate in between the vertical glass and the snake I keep that thermostat set at about 83*F just to be a little extra careful.

Even with the two heating mats, my ambient temperature probe which is set on the back in about the middle of the tank, is consistently reading about 65-70*F. I have tried covering half of the top with a towel to hold in a little more heat but it doesn't seem to help very much. I might be a little bit over-concerned but I would rather get a few more opinions that to just continue worrying about it. Pixie spend 95% of her time curled up leaning on the wall with the mini heat mat and sitting on the UTH, so basically the warmest part of the enclosure. She seems very healthy, and has been eating Hopper Mice for me every 5 days without issue, which I know is a good indicator of health for ball pythons.
I am currently using aspen shavings as a substrate (about 0.5 inch), but I'm considering switching to something that might hold heat and humidity better.

Let me know what you think about my setup/if you have any advice. If I can improve my husbandry in any way that will make Pixie happier and healthier, I'm all ears and ready to learn from your experience.

Thanks so much!