My baby is 11mos 1week old. I am breast feeding and afraid I am not producing enough. Is it okay to supplement with whole cow's milk between nursings?

Yes. A 1 year old baby can start whole cow milk. Breast milk is better. Formula is somewhat more nutritious than cow milk but is much more expensive. A baby who is a picky eater and eats little solid food, or has almost no variety in his choice of solid foods, will probably not get enough iron and vitamins from cow milk. Such a baby may be better off drinking breast milk + formula, instead of cow milk.
MILK FEEDINGS. Yes! it is about time to stop breast feeding and introduce cow's milk.