There's truly *no* rush to switch to the breastmilk of a cow before the minimum recommended 12 months (especially considering that constipation or diarrhea or dry/red skin or ear infections can crop up once baby switches over to cow's milk). Plus, AAP only recommends starting to wean AFTER the full 12 months of breastmilk is over if mom and/or baby desire. There's nothing wrong, and in fact a lot of health benefits for both baby AND mom, to continue breastfeeding past the 12 month mark (as long as mom isn't resenting every feeding - moms need to honor their own feelings/needs too!).
In your case, it sounds like are interested in stopping breastfeeding over the next few weeks --> so the way to go about that most safely for mom is to very gradually eliminate one feeding at a time. If you quit cold turkey, you run the risk of developing a plugged duct or getting an unexpected bout of mastitis... NOT fun... so that's totally avoidable by doing a very gradual weaning over several weeks. It's also a bit more gentle for baby to have a gradual weaning during which time you can replace your nursing time together with some other loving activity like cuddle time or book time. Check out the "How to Wean" section at the following link which I think gives some excellent tips for how to wean gently:
http://askdrsears.com/html/2/t026400.asp
Last but not least, CONGRATULATIONS on breastfeeding for 11 months - that is HUGE! I wish all women and babies could have that experience. In Ohio, by 6 months of age, only 11% of babies are breastfed, so hopefully that gives you some idea of just how much of an accomplishment your 11 months of breastfeeding really all. You have obviously worked diligentely and lovingly to provide breastmilk for your baby (even pumping in the bathroom stall - been there, done that, not the most pleasant place to pump, IMO)... how wonderful!!! Best of luck w/ the weaning - I hope it is a tender, beautiful ending to a wonderful breastfeeding relationship. :)