> For winter I got a standing tanning machine. Which I use 2-4x a week for 1 minute per use. I calculated this was equivalent to 5-15 minutes outside, depending on time, but engages the entirety of the bodies largest organ.

Excellent idea. In my temperate climate, I use the outdoor method, with one further tweak: Cover the head and arms, which get too much inadvertent exposure anyway during daily activity.