The stick on thermometers are trash, so don't waste your money. Big Apple pet supply has thermometer/hygrometer combos with probes.

What folks are hinting at, with the humidity issues, is that you may want to scrap the entire idea of getting a glass tank, and just order a solid-top reptile cage with front opening, locking doors. It will look awesome, and most of them come with built-in heat, so you just plug it into a thermostat, add the other stuff, and you're all set. When you factor in the cost of the heat pad, tank, and top, the cost of the solid-top cage isn't that much more, if you shop around. (I like Animal Plastics).

If not that, then consider using a plastic bin cage. The visiblity isn't that great, but the maintenance is tremendously easier. There are plenty of instructions around on how to adapt one.

The truth is, a glass tank with a screen top is just a high-maintenance, pain-the-neck enclosure for a ball python. It's really not suitable, so it's a lot of work to keep everything stable.