I don't know about store-bought lactose-free yogurt, but part of the Specific Carbohydrate Diet (SCD) is making homemade yogurt that is lactose-free. It is cultured longer than store-bought yogurt, (24-28 hours), which processes out the lactose.
I've had some non-dairy yogurt that has been pretty good. Essence of Life in Kensington and the I believe the Loblaws where Maple Leaf Gardens use to be carries some. The coconut based product by Soy Delicious was quite good.