this is the one I use, has more features than most. They do have other models with 9 "holiday" settings so you don't freeze when your off work for the weekday holidays. It does require a "common" wire from the furnace.
very sensitive, If I walk past it my tailwind will cause it to kick on when it's close to the offset temperature.
And yes, an offset of 2-3 degrees will prevent "short cycling" of your furnace.