Mishima by Philip Glass (Kronos Quartet plays Philip Glass would be a good bet). The album Asperities by Julia Kent, just out last year, is pretty phenomenal. Systems/Layers by Rachels and Vulnicura Strings by Björk might work. Soundtrack to Requiem for a Dream.
Note that there's an album of classical versions of Aphex songs by Alarm Will Sound which is very good (their Avril 14th is inferior though)
Avril 14th is one of my absolute favorite songs. It's my go-to song when I need to just relax and push away from reality for a bit; one of the few I can just put on repeat and be happy with.
Nils Frahm's Screws Reworked is usually tagged 'new classical' but certainly has roots in the same space as Avril 14th. New classical as a whole is an interesting genre.
Try Chilly Gonzales - Solo Piano (first one). Then try Erik Satie and John Cage. Then maybe Goldmund and Yann Tiersen (Amelie soundtrack). Then give up and go back to Richard.
I like all his albums but those songs are really some of the most relaxing sounds I have heard.