I'm interested in your light setup, particularly if you happen to use high-CRI bulbs.
It also took me ages to realize how large of an effect SAD had on me. I grew up in Texas, where it wasn't much of a thing, but went to college in Michigan and then moved to Germany (where I've been for 20 years) and it took me multiple years to notice the pattern of only struggling with what I'd previously dubbed "burn out" in the winter. That I used to visit Texas every Christmas masked the effect for a while since it gave me something of a reset during the shortest days of the year.
Now I manage with a combination of what I'd thought of as redonkulous amounts of lighting (20-ish bulbs in my living room, 7 in my small office), and usually 1+ months away from Berlin in the winter.
It's only been relatively recent that going to your extent in terms of lumens has been possible. I was previously pushing 1000w of halogen lighting in my living room, and going to a multiple of that felt like it got into extremely wasteful territory. (There is the reasonable counterargument that in winter, all of the lighting watts also heat the apartment, but I use my lighting setup for a lot of months where I don't also need heating...)
Do you also go for high-CRI bulbs? That's been a limiting factor for me at times is that I don't like the spectrum of cheaper LEDs (or CFLs) and often sourcing high-watt, high-CRI bulbs can be tricky. (I was late in switching to LEDs in general, having previously stockpiled halogen bulbs before they were banned in Europe, but a HN comment a couple years ago turned me on to high-CRI bulbs, which was a game-changer for me.)