You'll find 255/35's aren't too "thin", as far as ride harshness I can hardly notice the difference between them and the stocko's. If you look at the comparison pic the side wall is still quite tall.
As for option1 not having them, they don't show all the sizes on the site. If you email option1 during business hours (or contact them through their thread on here) you'll find they'll either have them or will be getting them in shortly. They order frequently and if they are out it wont be long until they have some again.
Again I highly recommend the 595's in 255/35's, they fit spot on.
FYI tyres fit differently depending on brand, for example Kumho KU31's in 255's look the same as 595's in 265's (too baggy for 9inches).
Have you considered the Kumho's??? I was going to get them in 245/35's until I saw the 595 255's on my rims, mmmmmm sexy!