Looking for a thermostate for our mueller climatrol furnace?what kind do I need?

You need to match it with the type of furnace you have: Gas, electric, or heat pump. Any good digital thermostat made for gas will work on a gas furnace, some are for both gas and electric, you just have to change a jumper for adapting it to the particular type of furnace. On a gas furnace the fan is controlled by a fan switch on the heat exchanger and on an electric furnace the fan comes on when the heat strips are energized.