2001 Jeep Cherokee Overheating

My car has recently been overheating. Since the first time this happened, I check my coolant at least every other day, and levels always seem normal. The gauge will read just slightly above 210 (though enough for me to notice the difference) then, suddenly, jump nearly to the red zone. The last two times this happened, the coolant backed into the reservoir until over-filling and spilling out. Since the coolant was actually bubbling, I thought that was a clear indication that it was, in fact, hot and not a misread of temperature on my gauge.
I'm assuming the cheapest and most obvious answer is thermostat. I will be purchasing one tomorrow, and replacing it (hopefully. With the help of Haynes). Does this sound like the best answer to my problem? Also, is the thermostat an easy fix?