is it absolutely neccesary to get a humidity measuring thermometer?
In a word, yes. The Accurite thermometers available at Walmart for $12 measure an in and an out temp (aka - hot and cold side) and they measure humidity.

If your humidity is too low, you'll have bad sheds. If it's too high, you could risk scale rot, RI, etc. It's better to spend $12 and keep your snake happy and healthy.

And I agree 100% about the ceramic bulb. If you're going to do overhead lighting, the CHE is the way to go. But I will always recommend under tank heaters since that's what I use and I guess you could say I'm biased.