The things that have not changed (enclosure and prey sizes) likely won't be the issue. The temps are low though- I suspect once you get those up, he'll get his appetite back.

A ball pushing 4 feet is probably adult and it is breeding (and brumating) season. So don't worry too much. If you are worried, you can buy an electronic scale to monitor his weight. I've heard 10% is an acceptable weight loss during a fast, assuming he isn't over/underweight to begin with (but don't quote me on that).