I recommend Ageless Spine, Lasting Health-- it's got a very sensible feedback system for improving posture and movement. The part I remember is moving your pelvis forward and backward and noticing what position makes your breathing easiest. This is an excellent feedback system for improvement. Possibly TMI, but I found it helped a lot to prevent constipation, something I never would have thought was a postural issue.

However, the author notes that this doesn't work for everyone, and at that point she recommends getting a teacher. I give a lot of credit to people who admit that their advice doesn't work for everyone.

She's got an updated version, but I don't know how different it is.

Uncommon Sensing offering one free Feldenkrais exercise (about forty minutes) per month. Not only are they good exercises (for the nervous system-- they aren't for challenging strength or endurance), but the one-a-month schedule eliminates the impediment of having to choose an exercise from the many available. One of them increased my hip mobility enough so that getting up on a bar stool became easy-- I'm very short, and this is the first that bar stools haven't been an annoyance.

Thanks for asking.