My central heating is hot water radiators, heated by natural gas furnace. Years ago to save money I set the thermostat at 55 and bought oil thermal space heaters for the rooms I use regularly. For rooms I only use temporarily, I use air blown heat, aim it at me, and turn it back off when I am finished in that room. I take my supplements regularly, and have not had a cold for years. Currently 82 with no co-morbidities.
There’s something to be said for ‘what works’... you’ve found what works for you. That’s great.
I’m allergic to flu shots... then realized in the many decades I’ve been here I’ve never once gotten the flu... so I don’t sweat it anymore. In my case it’s a mystery - or good luck or something I don’t control.