I second the "Man’s Search for Meaning" recommendation. That book is great for putting one's struggles into perspective, and emphasizing the importance of a "why."
This book gets recommended a lot probably because it relates to the Holocaust, but it's worth pointing out that "Man’s Search for Meaning" describes itself as "a story". It's not a philosophical book. If you want, you can learn about the development of human thought over time. There is an entire history of philosophy.
"Siddhartha" or "The Adventures of Huckleberry Finn" might also relate to the meaning of life but they are also not philosophy books. They might be great books but you might be looking for something completely different.
If you get the full edition, there’s a complete discourse on Frankl’s method (designed for the layperson). That said, I found the actual story of his experience far more compelling and much easier to relate to… at least in a way of making any problems I might have seem meaningless by comparison.
Interestingly I found the logotherapy part of the book much more useful and compelling. Using the holocaust as an example of putting it into practice is so extreme it's unrelatable. The daily life type case studies in the second part of the book were much easier for me to learn from. Saying that, hearing a first hand account of the holocaust was powerful in its own way.
The book is a personal reflection, but it’s also a distillation of “logotherapy,” which is both a philosophy and a therapeutic technique. If the book resonates with you, then looking into a more formal application of logotherapy would be a logical next step.
