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).
I love the winter for this. My thermostat is set to 16C at night. I prefer if the heat never even kicks on, it’s noisy and disruptive to have air blowing through the vents. I wish there was AC that could make my house that cold at night while making no noise!
I’m always colder in my mother’s house in Scotland (-5°C on cold days) than I am at my MIL’s house in the frozen Canadian wastelands (-40°C/F on cold days), because my mother will play games with thermostat to save money, where my MIL would simply die of exposure if the heating wasn’t on consistently for 6 months of the year.
Funny, I went the other way round in the Bay Area. PG&E bills were so high so it was the choice of putting on a jacket or paying $1k extra over the winter months. And my reasoning was "I can afford a jacket".