Milk is perfectly sufficient past 6 months. Yes, iron can run lower, but you don't see a lot of anemic babies running around at 6 months and 2 weeks or anything.
In fact, my baby was preemie (not as much iron stores), we started tasting solids around 6 months, but he is just now starting to eat more than two bites a day, and his pediatrician said he wouldn't worry if he wasn't eating too well at a year, as long as he was getting plenty of breastmilk. He said the will do a blood test for it at 12 months, but no need to worry.
Although breastmilk has less iron than formula, the iron is significantly more digestible than iron from other sources.