B.W.
I see your little one is just a month old... is there a reason you are stopping breastfeeding? Your body is still in 'make lotsa milk' mode, so stopping now will take time to wean your body down. I hate to see moms stopping nursing so soon, if you are having a problem I'm sure its something that can be fixed or helped.... I think we've all had every problem in the book nursing at one point or another. I would love to help out if you need it.
If you are set on weaning, do it SLOWLY! This soon after birth, you really need to do it slowly because not only will your baby need the time to get his body used to formula, but your body will hav a huge drop in hormones, and the 'feel good' hormone that goes along with breastfeeding will drop dramatically if you don't go slowly, making your more susceptable to PPD.
Drop one feeding for at least a week, then the next week drop another feeding, and so on. It should take you at least 4 weeks to wean totally, and you may have to pump for a couple weeks to wean your body fully.