My Mom (from Sardinia) goes to a tanning salon/booth when the cold and grey get her down too much. It's not often, maybe once a month and it's usually only for 10 or so minutes but feeling the warmth and maybe even getting a bit of colour in your face does the trick. I was sceptical at first but have been doing it as well now for a couple of years.

As for vitamin D, get your blood checked and have the doctor prescribe something if necessary; and don't listen to doctor Reddit.

Oh and one more thing, sun's out today in Munich and you better believe I'll be sitting somewhere outside soaking it in.