Hey Saltire, am 6ft too. I don't wear floor length dresses for this v reason! I did manage to get a long dress (evening) a couple of years ago. I haven't found any high street shop that does them long enough! Have you looked in Next Tall? I haven't looked recently myself though.
I'm going to a black tie party next Friday and have got a lovely knee length dress from Phase Eight the dimensions are ok i.e. The waist isn't too high, making it look empire.
Sure someone else will come along with more ideas x
The PierceIIFionda dresses in Debehams tend to be a good few inches longer than yer average long dress. They are the only ones I've found that I can wear a slight heel with and they still skim the floor.