me personally I would go cows milk or soy milk, and avoid the formula.
if your bubs has tried and tollerates a large variety of berries etc and you are worried about nutrient levels, make them a 'special' drink in the middle of the day, like a bluberry milkshake or something. there are heaps of smoothy recipies in toddler and fussy kids books that you can hide a multitude of good foods in.