I don't provide additional heat for my geckos, but my apartment stays a near constant 75F even in winter..though the coldest days/nights it may drop a couple degrees. I don't have control over the heat in my place which in some ways suck as i prefer a room temperature much lower than that. But my reptiles do well so can't complain too much.

If your room temperatures drop alot in winter, some flexwatt on a thermostat should be fine. Not sure you can find a CHE less than 100 watts which may be too much heat for a crested gecko so since you already have the flexwatt it may be more convenient to just use a strip of that for really cold nights. Or move the cage into the warmest room for the winter.
-----
PHLdyPayne