I cannot bring you my lady, but I can bring you someone who talks about what it means to "do" the Alexander Technique:
I found that I'm happier when standing. Just now, I have "bent" my monitor so I can look at it in a standing position. In that way, I can balance myself on my two feet.
Yet, bad habit takes over when I play the flute, and I bend my neck. I know it's bad because it hurts. What I did with my lady, I learned to say NO every time I'm bending my head forward. It's not easy. But I shall persevere.
You are right, bad posture gives you pain just on the side -where your boobs are. If you stand and balance yourself on your 2 feet, you automatically feel better. Alexander said not to force this movement, but to let the body do it. What you can do is to say no to the bad posture, and direct with your mind to balance the head, but NOT do it, just think it without engaging the muscles of the neck. That is a steep learning curve.
An alternative to standing is to lie down on the floor, with some books and a blanket on top, so you can lay your head comfortably. A few minutes of this each day will transform your posture. But it's a learning curve!
A reference book I bought to do it after my lady has come and gone is: The Posture Workout by Carolyn Nicholls who is a prof of A.T. in Bournemouth.
Hope this helps, Mic