Start with high-confidence zen buddhism books, then narrow by subgenre or adjacent topics.
The Wisdom of Insecurity
Alan Watts, Deepak Chopra MD
The Way of Zen
Alan Watts, Alan W. Watts
The Three Pillars of Zen
Philip Kapleau Roshi, Philip Kapleau
The Unfettered Mind
Takuan Soho, William Scott Wilson
Ordinary Wonder
Charlotte Joko Beck, Brenda Beck Hess
How to Sit
Thich Nhat Hanh