i dont think you understand the concept of a thermostat, how old are you? im not being disrespectful im just trying to establish details, thermostats control the heat source you are using to heat your enclosure,

1) you set the temperature on the thermostat,

2) you place the thermostat probe under or near the heat source

3) your temperatures are always stable as long as you maintain the probe in a decent place where it cant be moved by the snake

thermostats are a definite must have for any reptile keeper, if you do not have one you are risking fires, due to overheating, and harm or fatality of the animal, if you can not afford to buy the thermostat you should think if you can afford to keep the snake

if you use a heat lamp u probably need a low wattae bulb cos you have a reasonably small tank