Heat mat to light, snake not moving.

I just moved my snake to a different enclosure with an Arcadia halogen basking light with reflector lamp from an enclosure with a heat mat. He tried it out briefly at first but has barely moved for days and days apart from to come eat, he’s extremely still, and certainly no basking. I am going to try figure out how to get a heat mat in there but the way the substrate and drainage layer is built I can’t see how to have it outside, maybe I can come up with a way to put it inside the tank inside a box so he can’t touch it.

It has recently become very cold here and my house is like 14-16C quite often. I dunno if he just wants to hibernate. Any advice would be appreciated!