I would agree with Nettie that this would be a good book to help with your quest. It is practical, clear and well presented, and makes sense.
This may not be an issue for you, but, for example, in order to get more length down the front of the thigh, she has a simple exercise. You just lean forward a little, the thigh lengthens as you go back into upright, and you just maintain that position. Simples!
She uses boxes as a way of thinking about the position of the head, chest and pelvis in relation to each other, to help get a better balance.
The Pilates exercises include using a gym ball, which helps with posture and balance.
I am doing this from memory and not doing the book justice, but I hope it gives you some kind of flavour.
I liked also reading about her own story which was in part about frustration with her riding resulting in her becoming stronger and stronger with her aids, until she realised she was not the kind of rider she wanted to be. I believe that since then she is more influenced by the French classical school.
I have spent today with her and had 2 great sessions, one on postural alignment with exercises to improve balance and flexibility, and the second doing some Pilates for the horse; in-hand work.
I hope that is helpful to you.
All the best