Re: 10 month old transitioning to cows milk
congrats on making it almost to a year!
iron doesn't actually transfer well through breastmilk. this is why some pediatricians will recommend supplementing early, and worry about babies who aren't eating "enough" solids in their second 6 months, because of the concern they're not getting enough iron. these concerns are usually unfounded. in particular since you say he's eating what you eat - if he eats things with iron (leafy greens, meats, etc) then he's likely fine. babies generally are tested around 12 months for lead and anemia, anyway; if you're very concerned, you can ask your ped to put in the orders for that blood work right away.
i think the issue at hand is actually not the iron deficiency, but about how you feel about the nursing situation. are you happy with nursing only at night? are you working or separated from DS during the day, or why aren't you nursing him during the day? what makes you think you should introduce formula for 4 weeks?
and depending on what your nursing goals are ... there is no reason to wean your son at a year, if you (or he) don't want to. you can continue to nurse at night/whenever you're together, without pumping while you're away, and it's sure been an amazing parenting trick for me. if you do want to wean him, it sounds like you're on the way without much pain or tears, and that's great too.
Nursing, pumping, cloth-diapering, babywearing, working professor mama with the awesomest SAHD ever.