thermostat would be nice if your willing to pay for it...everyone I think has a different opinoin on this issue. Personally, I have a snake that has an UTH. I have no thermostat, and he is just fine. Corn snakes WILL move when they get hot to regulate their body temp. I do offer this snake extra aspen bedding.
If you want to add a heat light, please just make sure that your snake can't reach it and burn itself. Hope this helps you some.