For thermometer probes, they don't have to be stuck down at all. I just dangle mine close to the substrate when I use the probe ones. I have recently switched to these however, and it solves that problem.
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
you just put the whole unit in the tank, one on the hot side and one on the cold. I have them sitting on top of the substrate Astrid doesn't bother them. Some people attach them to the sides of the tank.
When you get your themostat, that probe will need to go between the heat mat and the bottom of the tank. If you have the stick on type heat mat, they are not designed to be peeled off, so you may have an issue. I don't use that kind so I don't have a lot of advice there.
ETA: above poster detailed a work around for that!