I was told by a sales person at John Lewis I should go for softer matteress as i'm quite tall (6ft) though I can't see how height determines what matteress you should use. I have some back problems right now though thats mainly because the matteress i'm currently using is well and truly past it.
That just sounds bizarre to me, the softer the matress the less support your back has, surely? I'm 6' 2" by the way.
Unless the soft matresses I've had have always been knackered.