I have an ExoTerra tank that came with a digital thermometer and half-canopy which contains a 'nightlight' which mimics moonlight:
So far, I've found that this is sufficient to maintain a fairly steady temperature but with winter on the way, I've invested in a second half-canopy to sit over the front. This contains a red bulb (as cresties can't see red) and it'll be plugged into a thermostat to deliver variable, gentle heat as required.
My crestie's viv varies between 18-19degC at night and up to 24-25degC in the summer. He seems to be quite happy with this and is doing very well. The white disc you can see on the back of the left-hand door is a hygrometer which measures humidity. I tend to let it fall to around 50% before misting and bringing it back up to around 70%. Misting is also a good way to cool the viv if it's a little on the warm side.
As I understand it, heat mats aren't really a very effective source of heat for a crestie. They prefer ambient warmth rather than localised heat sources such as heat mats.