I've read about the jhānas which one can experience from concentration (samatha) meditation. I have been practicing some form of mindfulness, breathing meditation, but have not experienced a state of absorption that is characteristic of the jhānas. I know that the jhānas cannot be experienced only by reading about them, however, the insight from my meditation practice alone has not brought me to them.
In the process of deepening meditation, one can roughly identify three distinct stages: the stage of concentration, the stage of meditation, and the stage of absorption.
This dualistic relationship is broken gradually as the practitioner moves into the stage of meditation. The ego-conscious activity is gradually lessened, and the barriers it set up for itself will gradually be removed. When the practitioner enters the stage of absorption, the dualistic framing of the mind will be removed such that the mind starts structuring itself non-dualistically. There will be no separation or distancing between an object of the mind and the activity of the mind itself.
I don't have the budget for every book on Zen Buddhism, but I have read all the Zen books on Kindle Unlimited (the content is mostly history, terminology, and sitting accessories). What books are there that go into depth on Zen/samatha meditation practice?