I've answered another question on posture on the Quora platform, where people ask the general public about anything and everything. This is the question I answered:
Why is nothing working for my cervical spine pain? I've done physical therapy for 2 years as well as fixing my posture, sleeping position, ice/heat therapy, medicine, and doing exercises every day. I don't know what else to try.
Can I question you on fixing your posture?
What is your definition of good posture, and how did you fix it?
Posture isn't a very good metric of how well you are using yourself, what you're wanting is poise. Posture is merely a shape, which if held with excess effort has no value at all. Poise is a quality that allows for subtle mobility of the spine. A healthy spine isn't “held" in place, but is mobile to allow you to keep spontaneously refinding the support provided by gravity. Gravity is your posture's best friend, it's the only reason you have, or need a posture, and contrary to public opinion, your posture isn't fighting against gravity, but actively using it to it's advantage. As counter-intuitive as it may currently seem, gravity isn't a force that is pulling you down, the ground reaction force is actually pushing you up, and with poise you can “surf" that up-thrust. We've known this for over 100 years since Einstein's Theory of General Relativity.
The picture you often see in articles about “good posture" showing someone side on with a plumb line connecting the ear, shoulder, hip, knee and ankle is very misleading. The article usually suggests you want to achieve this alignment, but that leads to rigidity, which takes excess effort leading either to sore muscles or an inability to maintain it. The picture is better understood if you take that plumb line to be the average around which you wobble. The skeleton is an intrinsically unstable structure, so whenever you're upright you're in movement. That movement is part of your natural balance mechanism, so you don't want to be fixed. The likelihood of finding and maintaining a fixed alignment that maximises the support of gravity is next to nothing, and meaningless as the movement of your head or arms requires you to find a new “perfect" alignment. And as soon as you start walking…
As to what else you can try, I recommend the Alexander Technique, which admittedly I'm biased towards because I teach it. However, Gold Standard research by the University of Southampton, funded by the UKs NHS, has shown that Alexander lessons are clinically effective for back pain. Renowned Spinal Neurosurgeon Jack Stern is also quoted as saying “97% of people with back pain could benefit by learning the Alexander Technique”.