I think I finally found a fix to my sleep. Or at least a quickfix.
Your brain reacts to light of day and night. It is hard to force yourself to not use artificial light at night. Obviously.
So, I am now trying a different route. Quite radical, but it seems to be working so far. I just leave the lights on during the day too. That way, no matter when will I finally find the willpower to stur lights down at night, there will always be the natural day-night cycle with stronger light uring the day.