Normally, I would say the heat mat should be just fine, esp. on a thermostat. Put his favorite hide above it and if he wants to be warm, he will get in there and curl up above that heat mat. As long as that area doesn't get more then 92, he will be good. That way you can turn the light bulb off, they can take a bit of a drop in ambient temps as long as they got a "warm spot".

Getting a little bit cooler then normal for a few hours, is better then getting to hot !

Has he eaten recently ?