I personally make coats so I can custom make on for you. I have had the same problem. Even my own yorkie is longer than my own standard size XXS but it fits perfect in the chest and neck on her. So I end up making her an xxs but 1 1/2 inch longer so it will cover her entire back. I think Yorkies are just long breeds. But anyways heres my website:
www.tinkerbellscloset.com