I used to take 4k IU + K² and think that I'm covered, since 4K units was a lot.
I landed on just above deficient when tested.
My wife was on kind of same regime, but didn't follow it very strictly. She was deficient, but not extremely.
It was quite surprising, because I got warned when buying 4k unit tabs that they were quite strong and pharmacy clerk suggested taking less.
Have you looked into UVB lamps?
Had a friend talking about them, but they seem to be prohibitively expensive. Do you have positive experience using such lamps?
I tend to have some eczema on my scalp that sun really helps with.
Maybe a lamp that costs the equivalent of a week of holidays in a warm place could be justified after all.
I don't have any experience myself but they do seem to be effective. Yeah, I think you'd have to compare it to a holiday, or how much time that would mean in a Solarium.