Holy shit, I never thought I'd see them mentioned in the wild, much less on this topic because that was going to be my reccomendation. Years ago I quit my drugging, was the most depressed I'd ever been, after years of hard abuse of the mind and body I couldn't find pleasure anymore. Music always has a profound effect on me so like OP I sought out new tunes to ease my mind and I stumbled upon Board of Canada which checked all the right boxes for me. I really connected with their dark moody and nostalgic tracks. It helped me feel something...not necessarily happiness per se, but it evoked emotions that I felt I had been missing, its just such a strange sound they have. Really soothed my mind in the following months and made me feel like I'd make it through.