Hi
An excellent article by Smith and Osullivan (I would add the link but some message on the forum blocks it and I can't seem to stop it with my limited technical knowledge!) gives an invaluable insight into the problems of posture.
They assessed 800 students and classified them into sway, lordotic, normal or flat. The students who had a spinal position that was classed as 'non neutral' were 20% more likely to have LBP (ie flexed or lordotic).

So how does this help? Dont just tell everyone to sit up unless they habitually sit in flexion and if they sit in a lordotic posture (usually perched on the edge of the chair and 'locked' into this position) tell them to flex and aim for a more normal or 'neutal' posture.

We are all different so give appropriate advice. Additionally I would save your money and not buy a fancy back support. Just move, get out of the chair regularly and exercise outside of work. Develop a bladder problem that necessitates you visiting the toilet regularly or fall in love with someone in a distant office! Just move.