I can't imagine breeding a 3.5 lb female. What if a gene from many generations back gets expressed and she has a puppy destined to be 13-15 pounds? What a disaster that would be.
You might try looking for breeder referrals from the YTCA. Or I'd highly recommend my breeder, Deb Sillers, who gives a 5 year health guarantee against life threatening illnesses such as liver shunt or heart defects, and 1 year for joints. She is a wonderful woman who has helped me so much raising my Cookie Monster, and believe me, I have had a million questions for her. I have had Cookie for a year now, and every vet exam her heart, hips, knees, everything pass with flying colors. Cook is such a lightning bug, she is an amazing hunter, and she has been such a sweet pup since I got her at 14.5 weeks. It's obvious Deb spent some real quality time with her, because from the second I got her she has been confident and loving around people. I just can't express how much joy the pup I got from her has brought me!
Amazing Yorkies - AKC Yorkie Show Breeder - Show Prospects or Quality Pets