M.L.
The American Academy of Pediatrics directs parents to feed children whole milk up to age two. More generally, the Academy recommends that parents do not restrict any fat or calorie intake for children under two years of age, except on the advice of your child's pediatrician, because fat is necessary for brain development.
My son & I are working on the switch to whole milk ourselves. We've been breast-feeding for a year, and supplementing with formula for the last month or so due to a decrease in milk supply, but I plan to phase out the formula in favor of the cow's milk.
My son is vehemently anti-sippy cup and we are also phasing out the bottle, so we're nursing morning & night, pumping once during the day and working on using a regular ole cup at meals & snacks. The cup is offered every time food is offered. It's messy, but he's starting to get the hang of it and I think he likes the fact that he has a cup- just like everyone else at the table. He takes it every time, regardless of what's in it (milk, water), and does his best. Perhaps your son wouldlike a cup? We're just going to take the transition slowly and see how it goes. Without using a bottle, it's hard to tell exactly how much fluid he's getting, so I monitor his wet diapers and bowel movements. As long as he has lots of wet diapers and no constipation, I think he's ok. But, I should mention that he's in the 50 percentile for weight, so I'm not as concerned about hitting that 16 oz mark as you are.
How is your son's eating? Sounds like he's a good drinker, if he's been nursing for 12 mos, but is he eating enough to keep pace with his energetic toddler lifestyle? Maybe that's a good place to introduce more of the calories and nutrients that he needs, as opposed to continuing formula. Though, I would do whatever my doctor suggested. Good luck!