For years I did this with the thermostat - something I learned from my father who always kept the house under 65F (18C) in Winter. I'm somewhat ashamed to admit it even led to arguments with my spouse early in our marriage when I would enter a room and find the thermostat set to a balmy 70F.
Eventually I just sat down, looked at how much it costs keep the house a few degrees warmer in winter, and realized we could afford to be comfortable. And if I were really hell bent on saving money, there were other lower-priority expenses I could cut back on first. But I don't even think it was even necessarily about the money - it was more that saving energy and toughing it out felt virtuous to me. Which is all fine, but not something that should be imposed on your partner if they don't share the same beliefs (or if they just get cold easier than you).
Eventually I just sat down, looked at how much it costs keep the house a few degrees warmer in winter, and realized we could afford to be comfortable. And if I were really hell bent on saving money, there were other lower-priority expenses I could cut back on first. But I don't even think it was even necessarily about the money - it was more that saving energy and toughing it out felt virtuous to me. Which is all fine, but not something that should be imposed on your partner if they don't share the same beliefs (or if they just get cold easier than you).