“Could you recommend a book about ānāpānasati or mindful approaches to the jhānas?” Answered by Ajahn Pasanno. [Mindfulness of breathing] [Jhāna] [Dhamma books]
Reference: Mindfulness with Breathing by Ajahn Buddhadāsa.
Reference: Breath by Breath: The Liberating Practice of Insight Meditation by Larry Rosenberg (commercial).
Reference: Beyond Mindfulness in Plain English: An Introductory Guide to Deeper States of Meditation by Bhante Gunaratana (commercial).
Note: More recent books about mindfulness of breathing from the Thai Forest Tradition include Keeping the Breath in Mind and Lessons in Samādhi by Ajahn Lee Dhammadharo, With Each and Every Breath by Ajahn Ṭhānissaro, and Breathing like a Buddha by Ajahn Sucitto.