If your lo is happy with 4 nursings and still eats 3 meals a day, why change? I just weaned my dd to 3 nursings and am reluctant to give up that other mid-day nursing, and she's over a year. She eats great, and has dairy milk once a day from a cup; water with meals. Don't worry about using the cup yet; keep offering it and I promise you, one day your lo will just take it. You can experiment with different types; my dd likes a straw-type cup for milk. I think that the sucking action from the straw is more like nursing. She uses the old-fashioned type of sippy with the free-flowing spout for water and has since 9 months.
And yes, at this age, your milk is much better for your lo than cow's milk!