Petco has an on/off thermostat I've only been able to find a rheostat at petsmart, best bet is online if u don't have good petstore. Btw the reason u can feed a little bigger is because of the freezing process, the bones are not as hard to squeeze and break making it easier to get a larger prey down, also when I say bigger, I don't mean if u feed pups it can take a wean, or if u have small rat u can go medium I mean one that is equal to or slighty larger then the width of the snake and if u happen to have to get a small rat but urs is on weaned then it should be ok, just keep in mind larger prey take longer to digest, so if u have been feeding 30 gram weaned then one that is several grams more isn't gonna hurt, just don't overfeed, and if a prey is too big they either won't eat it, or will most likely not finish eating