Either eclectic modern clinical psychology (introspective methods) or taoism. But both are hard to learn through texts sadly (anything important really is)
Trying out belief systems is like choosing programming languages: rather hard to appraise them without actually trying to build something and run it in your wetware computer.
From what I remember of Laozi, he also describes entering an indescribable state of mind. Zhuangzu also explores themes of accepting the world as is, and accepting death.
psych: https://www.amazon.com/Unlocking-Emotional-Brain-Eliminating... https://www.amazon.com/Gestalt-Therapy-Excitement-Growth-Per...
taoism: https://www.amazon.com/dp/B003T0G9E4/ref=dp-kindle-redirect?... but really, search for a master