You have a few choices. One is a Ranco thermostat, about $60.00 from www.herpsupplies.com. This is an ON-OFF device that will do what you stated, but it requires you to wire it up. If you're not comfortable with 115VAC wiring then don't get this controller. Another choice is Big Apple Herpetological's proportional controller, about $120.00. This is your best choice - it will hold the temperature very closely. Another choice is the A-Life thermostat, sold at various stores including Big Apple I think. This is an ON-OFF thermostat with a built-in 4 deg differential. It is about $40.00. Good luck.