Take a look at this article, it's very interesting:

http://cirrie.buffalo.edu/encyclopedia/en/article/190/

Or, if you want the TL;DR "executive summary": changing posture often is infinitely more important than a supposedly "good" posture.

Even maintaining a "correct" posture for prolonged periods of time is harmful.

It may sound funny, but doing the "pelvic thrust" movement often while you're sitting makes a HUGE difference to minimize the back pain. Of course, it's always better to get out of the chair every hour and do some exercises to flex and extend the spine. The more you move, the better.

Thanks for the link, interesting read.

I'm actually not too bad at keeping myself moving at my desk - shoulder rolls, etc. I stretch most nights to some degree and like I say I get a decent amount of exercise; I ride a pushbike to work so it's pretty low impact.

But I still wake up stiff and get headaches, etc, and I know it's back related. It's not a big deal at this stage, more just frustrating. I gotta do something though before it becomes a problem.