Did Lincoln Own Slaves? -Prokopowicz
It's about 300 pages but the format really lends its self to casually reading. The chapters are split into different parts of his life and within them are Q&A's, he lists additional info for his answers in case you want to read more on it. It's really light and enjoyable reading with tons of interesting questions!
Thinking, Fast and Slow -Kahneman
It's about 500 pages but one of the most book in pop Psychology. The author won a Nobel Prize in Econ for the work he goes over in it. This might not be your first read but I would definitely recommend you keep it in the shelf for when you're ready.