We're cowmilkfree, not lactosefree, but similar issues.

Allergen: milk is a key one! But it can be disguised as butter or other dairy products in ingredients. All but the darkest chocolate, or rice milk chocolate, is out too.

I made a vegan cheese sauce the other day, using olive oil instead of butter and soy milk and soy cream cheese. Olive oil for butter is always a good substitute, health-wise.