kefir is lactose free-- it is a cultured milk drink that tastes kind of like a yogurt smoothie. the kefir cultures break down the lactose.
cheese and yogurt are much easier to digest because they are cultured-- the culture breaks the milk down, but i'm not sure specifically whether it breaks down lactose or casein... but you might start with some organic yogurt and see how that goes. people with milk allergies (like me) do much better with cultured milk products.
goat milk is even gentler on the tummy because it is most similar to breastmilk. you can usually find goat milk at a health food store, or you can find a farm that offers goat shares.
i'm really sensitive to regular milk so we participate in a milk share program-- we buy a share of a dairy farm, and we get fresh raw milk. it's much easier for the body to digest because it has good bacteria that help digest the lactose. if you want to read more about it and find a source near you look at www.realmilk.com We drink both raw cow and goat milk. it is grass fed, organic, hormone free, clean and very tasty. the cream rises to the top... mmmm!