We set ours to 18.5 and we felt fine al winter by simply using warmer clothes at home than what we were used to. Your mileage will vary, but for the environment warmer clothes are much friendlier than warmer houses.
Try to do office work from home with a subpar temperature. I hate it and it's unhealthy. 20 celsius is a healthy temperature, I'm not taking anything less.
I'm sure it's uncomfortable, but I'm not sure why it would be unhealthy.
Well, I do work from home, so I worked all winter at 18.5 without issues. People are different.
Then question why to even stop lowering? Most parts of Europe never goes to extreme cold. No heating needed if you wear enough clothes.
Damp and raised relative humidty is neither healthy for the buildings envelope and the occupants