I wouldn't say it's the single solution, which might be because my depression wasn't limited by season. I'm speaking in the past tense because my depression is largely managed by diet and exercise (rock climbing). The diet aspect is basically covered by the AFS in Table 2 here[1], with some additional natural probiotics (frequent yogurt and occasional kombucha).
Like you, I basically figured this out with some luck in stumbling across information, some self-experimentation, and little help from medical professionals. What little help I did receive was in NY. In TN where I currently reside, I likely would not have received even that help, because medical care is unaffordable for most people. Additionally, there are an inordinate number of horror stories here about prescribers getting people onto a huge number of medications--this seems to particularly happen to young women who aren't comfortable advocating for themselves. I suspect this is due to pharmaceutical kickbacks, but haven't found any data to back that hypothesis up.