What a treat and a revelation to find this book: Coherence by Dr. Alan Watkins. Dr. Watkins (a cardiologist) has thought a lot about the connection between body and mind. He takes a deep look at how to improve your business results and energy management.
I don't know if Dr. Watkins himself would consider his book to be about mindfulness, necessarily. However the techniques recommneded in the first section are similar to mindful breathing techniques.
For the veteran of meditation, what will be interesting here is a focus on the physiological and some of Dr. Watkins' reasons 'why' it is importnat to engage in these practices. He is interested in your happiness, but the physiological mechanisms at play are something wholly different than you may have encountered.
I am only about 100 pages into it, but I am really enjoying it. More when I finish the book.