I keep my heating at the same level throughout the year, so it kicks in at a temperature I find comfortable. If X degrees is too cold in December, it's too cold in July. Mrs T and I usually wear sweaters, so we don't heat the house to a silly level.
That said, I've lowered it by a degree this autumn and it may go down further if the bills get out of control. We can wear the stuff we bought for our Hurtigruten cruise if necessary.