In the UK the minimum recommended milk from 1 year is 350mls (around 12 ounces) but I know the advice differs greatly depending on which country you live in. This minimum includes milk with cereal, milk in foods, dairy products (yoghurt/cheese, etc), etc so they dont have to take much milk as a drink any more.
My dd has a couple of ounces of milk to drink with her breakfast and a small cup of milk before bed (5/6 ounces) and that is all the milk she drinks. The rest of her intake is made up of the above substitutes.
I'm sure your lo is getting the nutrients he needs from the milk he does have and the yoghurts he is having as well.
Seona