Schumann wrote quite a bit of music that might work for that purpose. In Kinderszenen, for example, there are the very famous "Träumerei", and the less famous but even cheerier "Von fremden Ländern und Menschen".
Mendelssohn Bartholdy wrote his many songs without words, and several of them are well known.
Satie wrote the famous Gymnopedies, and the Gnossiennes. They might work well (although they evoke more mysterious feelings than pleasant ones).
Sheet music would be available from IMSLP.