Body shaper/slimmer

I have never had to buy one of these and need recommendations!

I have a wedding to go to, I will be 3 weeks Post partem. My belly is "almost" flat (I'm 2 weeks PP now) I need something that will give me my waist back, but at the same time, not flatten my booty. The dress I bought is black, size 2, a jersey knit material comes just above my knee. it's only tight on my chest and waist.

TIA for any suggestions!!!