The best book I could ever recommend you to read is the following: "Man's Search for Meaning" by Viktor Frankl.
It completely changed how I think and behave because it made me realize of what's really important in life.
It's a bit sad from time to times but it's totally worth it, specially if you're into books.
This sounds interesting? How dense is the book, I understand it wont be the easiest of read but I recently read The selfish gene and want something a little easier to digest.