In reply to goosebump:
Hi,
my workplace use these people; give them a ring, they should be able to sort you out with fitting and a sample. We tend to go for a simple "Ergo Plus" chair with extra lumbar support, , Extra high back, seat slide (to accommodate peeps with really long legs) and NO ARMS. It should come in at 2-300 quid.
http://www.godfreysyrett.co.uk/products.shtml
Sx