From what I remember of my teen years, I read a lot of The Chalet School, Agatha Christie, Jean Plaidy, Catherine Cookson and some of the classics. I used to go to the library very often. I remember feeling a bit lost in the adult section when I went there first. There was no YA back then, I don't think.
6.The Betrayal: Helen Dunmore.
This is the second book in a short series, but can be read as a standalone novel.
Leningrad, 1952, Andrei, a young doctor, and Anna, a nursery school teacher, are busy working and rebuilding their lives in this fragile post-war era. They, like their fellow citizens, keep their heads down to avoid the scrutiny of Stalin's Ministry of State Security. However, when Andrei is asked to treat the seriously sick child of a secret police officer, he is fearful of being put in an impossible position that could compromise his credentials as a doctor, his freedom, and even his life.
A friend gave me her copy of this and assured me that it was very good, and she wasn't wrong. The build-up of suspense, the creeping dread and unimaginable fears of people living under a totalitarian regime are powerfully evoked. It's a good read if you are interested in this era.