Q: are Sherlock Holmes stories mysteries? The reader can't really solve them. Information is held back. This is not that case with Christie books. The clues are there if you can put them together.
My first mysteries were the Happy Hollisters series.
Anyone else remember Pete, Pam, Ricky, Holly and Sue?
As to adult fare, Miss Marple stories by Agatha Christie (pinging our own Miss M!) and I do consider Sherlock Holmes to be mysteries.
I need to ponder something to recommend that might be different.
(I have lots of Perry Mason paperbacks I got from my grandmother...I read them all when I first acquired them years ago...)