Temperature controlled switch - Extreme TEMPS

Hi,
I need a temperature controlled switch/relay that will active at a given temperature. I need a really basic circuit.
The big problem is that I need the switch to activate at temperatures of -15/-20 degC. so the range must be from -30 to +30degC.
Anyone has ever worked on something similar ?
Thanks !

-30 to +30 degC are not extreme temps. See the app notes for LM35 and similar devices.

Yeah.. you're right.. but most "off the shelves" controllers don't cover under 0degC...
Maybe "awkward" temps would've applied more...

I've seen the LM35 in other posts... I'll take a closer look at it.. Thanks !!