I never considered using a slicker brush on a Yorkie (for the reasons Nancy listed) until Les Poochs sent me a "finishing" slicker, and one of the groomers here confirmed that she uses the same brush on her cotton coat Yorkie. After testing on my boys, I do like it for finishing.
Slickers do remove undercoat, but a good slicker will not damage your dog's coat. Reading in a groomer's forum, the two most popular slickers are Les Poochs and Doggyman. I no longer carry the Les Pooch in my store, but I do have the Doggyman, which is considerably less $$.
If your pup has really tight mats, you are going to have to carefully detangle those. I use a detangler (Pet Silk Silk Serum or simple corn starch) and the tail of a rat tail comb (from Mimimomo at her site
toplinepet.com)
If you are interested, take 10% off with coupon code LUVYT:
Doggyman Small Slicker Dog Brush