Many different thermostats can be used with a heater or heat exchanger.  This one is affordable, fully electronic and adjustable.  It reads in either Fahrenheit or Celsius, and can be adjusted for different degrees of hysteresis.  In other words it can be set to keep the temperature tightly controlled within 1 degree or can turn the heater on after a change of 4 degrees.  Be careful of thermostats that use a gas bulb for temperature sensing.  They may work just fine, but the thin copper tube between the gas bulb and thermostat is easily broken.  This one uses a simple thermocouple connected to the thermostat via a standard flexible wire.