45 years or so ago, I had a Boa Constrictor and was told the proper heat was to be around 91 degrees. I had a heat pad, but I didn't bother to get a thermostat. To be honest I don't even know if anyone was making reptile thermostats back then, I was about 17 years old at the time.
I plugged up the heat pad and of course without a thermostat it ran "Wide Open all the time." I took a day or two to play around with it and discovered if I placed about an inch of newspapers on top of it, the temp on top pf the newspapers was the temp I was looking for, 91 degrees. I continued to use newspaper as my substrate for many many years. I had that snake for 23 years, and she eventually was over 10 feet long when she finally passed away.
I had to move her into larger tanks as she grew, and I continued to use the same set up.
It was later on when I got my Cal King that I got my first thermostat. Actually it was a rheostat, but it too worked fine.
Today I have a Spider Robotics (Link:
https://www.spyderrobotics.com/index...products_id=26) and I have no problem with it either.
The bottom line is: No thermostat at all will work fine as long as you can dissipate the heat correctly, or a Cheap rheostat will work too, or you can spend a bundle and go top of the line. No matter what you do, "You Should have a reliable Infrared Thermometer that you can measure the heat with" and you should do so frequently, even with the Top of the Line models.