General

Most of Brian Eno immediately relaxes me, especially the ambient stuff. Panda Bear’ Person Pitch too, I play that at least once a week.

I discovered (years too late) the soothing qualities of old English Folk music.
I play acoustic guitar, and have started learning many of these classic songs.
Have a listen to music by the late 60's to early 70's band 'Pentangle', and also to two of it's members solo albums, John Renbourn, & Bert Jansch, you might enjoy it.

The Icelandic post-rock band "Sigur Ros" has some slower, more instrumental works. See the album "Valtari" or "Riceboy Sleeps". It hits a soulful spot for me.