Particularly the history of Jewish people in Eastern Europe (with an emphasis of the Polish-Lithuanian Commonwealth).
Everything I find is World War II/Holocaust focused, but I want something more on the life in a shtetl, the history of how Jews came to be such a large part of the eastern European demography, and how they interacted with Polish nobility.
For general reference I would recommend The YIVO Encyclopedia of Jews in Eastern Europe.
Here is the online encyclopedia: https://yivoencyclopedia.org/
I would also suggest The Jews in Poland and Russia, Volume I, by Antony Polansky. It covers Jewish history in Eastern Europe in detail from 1350 to 1881. Amazon: https://www.amazon.com/Jews-Poland-Russia-vol-1350/dp/1874774641