I'm really bad at sitting properly and had some firm words from my osteo about posture, usually lie sideways on the sofa and sit on one leg.
I was recommended a lumbar roll and sloped cushion for my work chair and, although I was sceptical, it really did make a difference and my back was a lot happier. I get it at the middle of my lower back and the back of my neck and shoulderblades though quite possibly my arthritis playing a part as had abnormailities show up on xrays. I hunch over my desk as well which is really bad and really have to try and keep myself in check.
My osteo once said for me to rotate my lower arms from my elbow, just turn them in circles. He then said to stand up straight, roll my shoulders back etc... and do it again and see the difference, that proved a point :)