Honestly, those little dial thermometers are crap. Get the digital thermometer in there.. and anyway, a temp of 99 on the glass is too high. Thermostats are extremely important.

The dangers of feeding live are highly overrated. Adam here has something like 250 ball pythons that he feeds live every week.. for years and years with no problems. As long as you don't leave the mouse/rat in there with the snake for a crazy amount of time, there is nothing to worry over. However, if YOU prefer frozen, by all means go that route. I feed mine frozen thawed.. except for the select few who won't eat it.