The songs I know here are calming and the others seem so as well. I wracked my brain to come up with songs that might be comforting for people less pessimistic than me (heck, I find Nico relaxing). Here are two:

B. J. Thomas's cover of a Brian Wilson song: https://youtu.be/I_aB7I4lI6E

Glenn Campbell's cover of a Lou Reed song: https://youtu.be/pswsY37a1iA