just be sure to NOT handle for 2-3 days after the snake eats or it'll regurge.
you reeeaaally wanna invest in a digital thermometer as soon as humanly possible, borrow the money & pay it back when you can if you have to. the best thing for checking temps would by far be a temp gun. that will tell you the surface temps & thats how you'll know what your snake is sitting on all the time. for $40 you can get a temp gun & a metal case for it that comes with an extra battery, at tempgun.com.
i dont think anything was mentioned about this but what do you have providing the heat? a lamp or a heat pad? if its a heat pad you have it hooked up to a thermostat right? if a heat pad is not controlled by something like a thermostat it'll get too hot & could burn the snake.