Another thing you can try is to use red to near infrared light which has been shown to affect the mitochondrial electron transport chain. I read "Brain Photobiomodulation Therapy: A Narrative Review" a couple of days ago which is pretty interesting.
It may be a risky, but given that people that work outside have half the risk of melanoma as people who work indoors, I think regular low dose UV exposure may be a net positive even for cancer risk.
Spending 5 minutes under UV lamps is a guaranteed way to get a huge dose reasonably safely, and you will know the effect almost immediately. The vitamin D seems to be maintained for 2-3 weeks after as well.
The salons call the cheap machines “sun burning” machines to up sell the more expensive “browning beds”, but just use that cheap machine and only use it for say 5 minutes instead of the max 20.
I also cover my face. I am in no way noticeably tan after years of doing this, and the low dose protocol I use makes my body similar to the color my forearms are from normal sun exposure.
I hope that is helpful, and it was years ago that I was evaluating the risks and I don’t have the exact figures anymore, but you can lookup the UV profile of the bulbs that are in the machine. Just google search the numbers on the bulb.
Honestly the best thing vitamin D has going for it is being super inexpensive and safe. Because of that you can supplement vitamin D for almost any reason and expect to see at worst a very small cost (someone up thread said 3 cents a day, which seems in the ball park) and at best a significant subjective benefit (even if it's from a placebo effect).