The hygrometer I use is one from Walmart. It's in the Indoor/Outdoor thermometer section, and it's a little grey square digital one, and it'll measure the temps(at the unit and also at the end of a lone probe wire you can put on the other end of the tank) and also the humidity. The cost is around $14 I think, so it's pretty cheap. I've got a dozen around here for various bins and enclosures. Once in a while you get a bum one and have to go exchange it.
The pic isn't showing up for me. You're right in the research. Sometimes the inormation you get can contradict what you found elsewhere, so asking a ton of folks who all keep the species you have is ideal, which is why I love this site.
Using a heat mat without a thermostat can be risky. I don't know what your ambiant temps are, but you might wait until monday to get the new thermostat to use the heat mat. Some of them can shoot temps up to 120F without regulation from a thermostat.
Good luck!
Hah! You edited when I posted! This is the link I got to your pic I think... http://www.flickr.com/photos/rikster...in/photostream
You want to watch the exposed bulb so she doesn't get onto it. It LOOKS high enough that she won't be able to reach, but it's hard to tell. She needs hides that are a bit more secure, instead of the half log(unless you stuff the end with the moss which will "close" one end. One hide on cool end, one on hot end usually works well so the snake can choose to hide on either side. It's a very pretty cage.