I spent alot of money try to improve my posture but only two things really helped. Biofeedback to train me how the mucsles felt when they were relaxed. It took me 4 biofeedback trainers before I found one that helped me.

the other thing that helped was having PT's train me how to activate the muscles involved in good posture as I could no longer voluntarily active them. One muscle was the lougus colli and the other was a muscle close to the spine in the mid to low back that helps bring down the shoulder blade so the muscles in the upper shoulder and neck can relax. they also gave me strengthening exercise I could actually do without flaring.