There are many option ... what you need is an adjustable simple bimetal
strip .... these can be found for switching aquarium heaters, home
brew tanks, PCB etch tanks etc ... I would imagine MAPLIn etc. would
have what you want.
Alternativly get a standard home heating system Frost stat ...
Honeywell for example, you set the temp it switches at .
the contacs are just that ... contacts so can use on 12V with no
problem.
Just watch the current though as they are only designed for pumps or
M.valves.
>> Stay informed about: thermostat