I think your temps are fine if they hold at 75 and 90, 75 is not as horrible as people think as long as it has that 90 spot to thermo-regulate itself, plus he is still eating semi-regularly and not stopping all together. my concern is what your humidity is like since it sounds like that would be the variable right now that I can see being all over the place due to your heat set up and the time of year.

If your goal is to have him get more food, I would stick to rats instead of mice if he continues to go a couple weeks between feedings. like it was mentioned above, most slow down their eating in the winter months but as long as there is drastic change in weight this is fine. Very nice looking BP, I like the white that creeps up on the brown spots like a calico.