Man's Search for Meaning, Viktor Frankl
A Power of Your Own, Nikki Groom
Essentialism, The Disciplined Pursuit of Less, Greg McKeown 
Lisa Nichols YouTube channel (from conversation with Traci, S3E3)

Dr. Joe Dispenza YouTube channel - self-help (from conversation with Sarah, S3E5)

Untethered Soul, Michael Singer (from conversation with Sarah, S3E5)

The Artists Way, Julia Cameron (from 31. Amelie)