I'm not an expert, although I've been and still am in similar problems. But I think, although it varies from people to people, it's important that the game demands your undivided attention.
That's the reason a lot of people here is recommending Souls games, because when you play hard games, you have to be really focused, and thus you don't have time to think in something else.
Souls games work for me too, but it's a risky decision, because they can frustrate you a lot and not improving the situation.
That's the reason, for me the best option is puzzle games. They demand (usually) only your brain, not skill dependant (and your brain is what you want to target and distract), they give you plenty of reward feeling, and they are usually relaxing in graphics and music.
It's true that some puzzle games can be really difficult and frustrating, but if you chose carefully, they are a great option.
For me, that game is A Monster's Expedition. It's a really beautiful, soothing game, with the perfect challenge and, although it may sound weird in a puzzle game, it has the perfect pacing. Basically it's an open world, no level selection menu, and that means you always have several open routes if you get stuck, and, when you face a tough puzzle, usually they give you a couple easier afterwards to boost your confidence. It's extremely well design, with plenty of personality, and again, really soothing. The sounds of the sea, the trees... The gamefeel is perfect.
I know puzzle games are not everyone's cup of tea, but for this situations I think they really help.