Thermostats automatically adjust the power going to a heating source, keeping the temperature within a few degrees at all times. You still have to adjust the thermostat at night, unless you get one with an automatic night-drop.
This is an inexpensive thermostat, but you have o look it up on Google:
R-Zilla Controller Temperature 1000-Watt Thermostat Pet Reptile Supply Safe New
It's not new and it's not entirely safe. You can make it safer by never using more than 500 watts with this thermostat. 500 watts is plenty, even for a large habitat because you are controlling the heat in a restricted hot zone. But it's affordable, and it's a way out of the heating control problem. There are several other "cheap thermostats" (a Google search term) for you to look at, but AFIK, Zilla has the most to gain by making one that does not melt down.
The "safe" thermostats are solid-state so they don't have physical contacts that touch and un-touch (i.e. make-and-beak). You should look at those too.