I was actually just finding playlists on spotify with classical piano music! I know you didn't specifically ask for piano music, but here's my spotify playlist with tracks that are really wonderful and relaxing:
Clicky~
If you don't have spotify, here are the names of the tracks:
Sunderland - Federica Fornabaio
Chopin: Etude no. 11 In A Minor op.25-11 "Winter wind" - Tatiana Shebanova
Mozart: Fantasy in D Minor K397
La valse d'Amélie - Yann Tiersen
Chopin: Trois Nouvelles Etudes No.1 in F Minor Op.posth - Zbigniew Raubo
Schumann: Children Scenes Op 15 Child Falling Asleep - Robert Schumann, The London Festival Orchestra
Schumann: Children Scenes Op 15 From Foreign Lands and People - Robert Schumann, The London Festival Orchestra
Chopin: Mazurka no.25 in B Minor Op.33-4 - Rem Urasin
Comptine d'un autre été, l'après-midi - Yann Tiersen
Chopin: Etude no.3 in E Major Op.10-3 - Tatiana Shebanova
Chopin: Mazurka no.41 in C Sharp Minor Op 63 No.3 - The London Festival Orchestra
Chopin: Prelude no.4 in E Minor Op.28 - The London Festival Orchestra
Chopin: Prelude no.20 in C Minor Op.28 - The London Festival Orchestra
Ora, domani, mai più - Federica Fornabaio
L'ossessione del mare - Federica Fornabaio
Some of those tracks aren't classical, but still very relaxing.
I also love Schubert's 'Du bist die Ruh'. It's on Spotify, sung by Barbara Bonney. It's absolutely beautiful.