Did you ever consider a Biewer Yorkie? I just recently saw some pics on a thread entitled I was in Yorkie heaven - I went to the ladies website
www.stellaryorkies.com - she's a YT member here and seems to be very knowledgeable and her puppies, both Yorkies and Biewers, are beautiful. To me they seem to be a mix of Maltese and Yorkie, but the true Biewers come from Germany and have purebred papers.