- Man's Search For Meaning by Viktor Frankl (existential psychologist and holocaust survivor - some principles of finding meaning in life's circumstances from someone who went through a concentration camp)
- 12 Rules for Life by Jordan Peterson (Despite the politicized figure he became, the book is more about finding meaning in adopting responsibility with each rule being an example of how to do so)
- Subtle Art of Not Giving A F*ck by Mark Mason (light hearted self help, but some nice principles in it)
- Meditations by Marcus Aurelius (a little dated, but contains some nice aphorisms. Audible has a really great version read by Richard Armitage, the guy who played Thorin in the Hobbtit)
- Give the New Testament a shot (not everyone's cup of tea, but several billion have found it helpful in finding a meaningful life so its probably worth a shot)
Also, don't neglect audio books! I've found going for walkins while listening to these kind of books a great way to relax and reflect.