http://www.shineoncoat.co.uk/I bought two of these for my dogs. Fortunately the lady who makes them lives not too far away and she measured them up--I can't say I would have trusted myself to do it.
One dog loathes his and tries to walk around wearing it without much success, so I never put it on him. The younger dog is smart enough to know that he can go to sleep on the duvet and wake up nice and relaxed. I don't use it that often, but it does make a difference and would recommend them. We have the 'old' design with flaps for the ears, which the dogs tend to rub off, but there is a new design without this and it's a bit cheaper.