Here are some helpful, and sometimes amazing, websites dedicated to sacred music. I hope you see some you haven’t discovered yet!
Websites dedicated to hymns and sacred music
Liber Hymnarius – has many recordings of Latin hymns from the Divine Office
Preces-Latinae.org – a list of the Latin hymns for each hour of the Breviary
Catholic Hymnal: A Collection of Standard Catholic Hymns (1920)
St. Gregory Hymnal and Catholic Choir Book (1920)
St. Pius X Hymnal (1953) (Two editions are available here: organist/choir and congregation.)
Hymnal: A Supplement to Music First and Second Year