Overcoming Poor Posture
A Systematic Approach to Refining Your Posture for Health and Performance
Quite light on content, but it does contain a decent amount of helpful information and exercises, especially if you are new to this sort of thing. I suggest following along physically when you hit the exercise explanations.
To be honest, mainly purchased (new) to support Low, as I've read a lot of his advice over years and haven't bought Overcoming Gravity yet. The other reason I went for it is that I got a standing desk and have been interested in maintaining/improving my posture.