Brownsfan and Twoleftears gave you some good info. Them and Discogs. With Discogs you’ll probably pay $2-3 a disc. I’m also 69 and was introduced to classical in college by another student who did a good job introducing me. So here’s my plan. Find a copy of Ted Libbey’s “NPR Guide to Building a Classical CD Collection.” How’s that for right up your alley?
Since you liked the church music, why not get E. Power Biggs Plays Bach in the Thomaskirche. That’s a Columbia Masterworks release, which are always reliable. Mine is on vinyl, but open a Discogs account and look. Bach is a great place to start, so get the Brandenburg Concertos. I bet Neville Marriner and The Orchestra of St. Martin’s in the Fields has a good recording. That puts you in the Baroque era. Vivaldi, Telemann, Corelli are all representative. Before them are Dowland, Tallis, Byrd.
next is Classical era. Find Hayden’s last few symphonies, No. 99-104. Then Mozart (I’m going forward in time here), late symphonies No. 36-41, piano concerto 17, 20, 21, opera overtures (Marriner again) Clarinet Concerto (Anthony Pay), horn concertos. Beethoven symphonies — directors von Karajan, Bernstein, Bohm all good — piano concertos, No. 5 is the biggie, 1-4 good, too. Violin concerto.
I need to condense. Getting into Romantics. Chopin, Etudes, Waltzes, piano concerto 2; Tchaikovsky Sym. 4-6, piano concerto 1; Dvorak, Sym. 9, Smetana, The Moldau; Wagner, opera overtures only; Mendelssohn, Midsummer Nights Dream, Violin concerto, Sym. 3; Brahms, Sym. 4, piano concerto 2; Rimsky-Korsakov, Pictures at an Exhibition; Respighi, The Pines of Rome, Ancient Airs and Dances; Mahler, Sym. 1,4, 5. Holst, The Planets
flying fast. Prokofiev, Sym. 1, piano concerto 3; Rachmaninov, Rhapsody on a theme by Paganini, piano concertos 2-3; Stravinsky, Rite of Spring, The Firebird, Petroushka; Vaughan Williams, Greensleeves, The Lark Ascending, Variations on a theme by Thomas Tallis; Carl Orff, Carmina Burana; Gorecki, Sym. 3 (Sorrowful Songs); Arvo Part, Tabula Rasa, Sym. 3.
Should have just left it at the Libbey book! Cheers.