Can I suggest you see if you can adjust the existing seat more effectively? Try the pages around this link and you might not need to buy a backrest

Drive a Mazda 5 or 6. Lots of driver leg room. I get the same problem if I drive cars with wide transmission tunnels, which impinge on my left leg. BMW and VW are the worst for me. The centre console on Mk5 golf's and A3's actually bruise the outside of my left knee on any journey more than thirty miles.

It's Focus III TDCi 1.6, 2008 model, so not due for a replacement until 2012. The only part of my sitting environment which I cannot adjust for comfort - other than up-down - is the head restraints. To my (non-expert) way of thinking, the head restraint should at least try to follow the contours of the head, or am I missing something? If there is a fairly even gap between my skull and the restraint, in the event of a rear end collision, the ideal result should surely be that all the surface area of my head (maybe even my neck) hits the restraint evenly, rather than just a hefty whack at the top of my skull - which is what I get regularly on a normal journey!

A previous company car - a Vectra - had the same pivoting system as Saabs, whereby the restraint was not too close, but in the event of a rear ender, the pressure of the upper back against the seatback would have the effect of pushing the restraint forward to provide maximum support and protection from whiplash. It strikes me that this is a relatively low cost solution which is simply ignored by manufacturers to save a few pennies.