>The most significant factor influencing thermal comfort - even more important than air temperature and clothing - is human activity or body heat production (the metabolic rate). For instance, while it takes 12 clo-units to keep a resting person warm at an extremely low temperature of minus 40° C, this comes down to only 4 clo when this person is walking, and to only 1.25 clo when this person is running at 16 km/h. One of the most obvious reasons why our forefathers could bear lower indoor temperatures, was that they were more physically active than many of us.

To use that to one's advantage:

A little colder environment (e.g 18C/64F) than your comfort zone (e.g. 22C/72F) at normal humidity reminds you taking little breaks and be active during the day, it doesn't take much ("active recovery": 40-70% of your heart max; depending on your fitness status) and it goes a long way.

If you include the cognitive benefits/enhancement you get from deliberate short breaks instead of grinding hours away sitting in front of a screen, I struggle to really see a need to hack our biological design for a little colder environment. (sitting in a loose T and shorts outfit through trial and error I found out that I begin to feel noticeable uncomfortable at about 14-16C depending on my activity level throughout the day; I set my thermostat usually 1-2 degree above that (16C-18C) in accordance to the indoor humidity levels.)

Our bodies are extremely efficient [0] at regulating body temperature if one is cognizant of the instruction manual inherited through our evolution history.

Incorporating some High-Intensity/Resistance training gives an additional metabolic boost/afterburn which - no surprise here - synergistically couples itself with low-intensity/active recovery mode.

A bonus would be to expose yourself deliberately to extreme cold for a very short period of time (working your way slowly up). I personally don't go for numbers here but rather for the regular experience of real cold hitting your body and shifting some powerful gears (similar to an appreciation of "hunger" after a fast).

[0]https://en.m.wikipedia.org/wiki/Brown_adipose_tissue#Functio...