Breastmilk has dha.
No need to supplement with formula, breastmilk has more nutrients than formula and these nutrients are more easily absorbed.
As long as baby is eating a variety of food you shouldn't need to worry about iron. Otherwise you can try cooking soups with meat in it, or make nuggets or meatballs. Broccoli is a great source of iron which is has a higher absorbency when cooked than spinach. But really, there is no need to worry about iron levels unless baby is not eating anything at all.