Thanks for all your help and suggestions with this. I might pop back down to the market and see if there are any Minolta Autocords, as this has been recommended in quite a few replies.
I've used a Mamiya C330 in the past (in fact, I produced one of my degree show projects on one), so that's also worth considering.
One of the main reasons I was considering the Yashica and Rollei was because I wanted the discipline of the fixed standard lens, so I'm not too concerned with interchangeable lenses - perhaps I should have thought to mention that at the start! I think it must be the hayfever clogging up my brain...