http://spyderrobotics.com/home/products.html

they make a number of products any of which will work. I personally would strongly recommend a unit with the 'safety relay' feature. In the event of a controller fail it will kill the power rather than failing full power as most proportional stats do.

My second recommendation is a second on/off type thermostat (like this one for example https://www.hydrofarm.com/p/MTPRTC)

This can be used as a fail safe. The herpstat plugs its power into the on/off. The herpstat is set to a correct hot spot and the on off is set to a never get over this temperature (i use 100ºF). The reason is racks hold multiple animals so there is a lot on the line. The sliding system works well although sliding over a probe can and has at time pulled the probe free of the heat source. The probe goes cold the primary stat powers up to heat the probe that will not heat. Then the secondary with a probe at a different location now reaches its shut down temp and powers off the primary. This cycle can continue until noticed usually the herpstat will be squeaking its alarm so usually as soon as you check it is caught.

A second line of defence.

Something to keep in mind as well is racks are poor insulators they don't hold ambients well at all. Often racks are kept in spaces (rooms, closest or perhaps a rack in a cabinet of some sort) heated to the correct ambient temperatures.