I played Neir replicant this year and was blown away by how absolutely amazing the soundtrack is, it's not just soothing or relaxing but also fitting. Like, the stars aligned with this and the way they implemented the music to certain areas as well as add in the sound effects of certain areas and enemies into the tracks that play at specific points was genius, posting the OST on here won't do it justice, you just need to play the game. Playing the game with headphones on is very Zen. 

This one specific title sums the OST up and it is basically just for ONE small feild you cross a bit regularly in the game and it's perfect...

And Neir Automata too, might even be a better choice for relaxation... I never forget this one, the OST holds up on it's own...

The entire soundtrack of Hollow Knight is just gorgeous. 10/10 material.