During my first pregnancy I had several experienced mothers tell me to use a girdle after I delivered. I was pretty appalled - I hate constrictive clothing and besides, isn't that what diet and exercise are for?
Well, a week after my C-Section I ventured out to find something to put everything back where it belonged. The trying on phase was excrutiating, but when I found the right piece of shapewear I felt so much better! I bought both colors in this Spanx shaper and wore them constantly, whether out and about or kicking back with baby they were my constant companions. After about 8 weeks my body was nearly back to normal and I retired the shapers.
Trust me, this isn't just a vanity thing, the remainder of your baby belly is pretty uncomfortable especially if you had a C-section.
I would advise to go ahead and buy something like this while you are expecting so that you'll have it ready after delivery. Just buy a size up from your regular pre-pregnancy size to allow for your baby belly.