The Charlie Chan mysteries by Earl Derr Biggers. 6 total books. Stand alones. Written in the 1920’s. Golden Age mysteries and great fun.
The Brother Cadfael series by Ellis Peters. One of my favorite mystery series. Good mysteries, and good moral comments on the spiritual side of life. Not preachy though.
The Sherlock Holmes canon. Always a good go-to for any mystery lover.
Georgette Heyer’s mysteries. She’s better known for her regencies, but her mysteries (written in the 1930’s-1950’s) are pretty good and also Golden Age. Veddy, veddy British!!
The Philo Vance mysteries by S.S. Van Dine. Golden Age mysteries written in the 1920’s, 30’s, etc. The character of Philo you will either love or hate. He takes some getting used to.
Hope this helps! Happy reading.