Straight up

One of the residual effects of pregnancy has been that I don't know how to stand (or sit) straight. My posture is horrible. I'm either completely hunched over (as if I'm carrying a baby in my arms) or hyper-extended backwards (as if I'm carrying a baby in my belly). I don't even know where my center line is anymore. Maybe I should invest in one of those yoga ball chairs -- that will force me to sit correctly, won't it? Either that, or I will constantly fall off my chair at work, which would at least provide some comic relief to my coworkers.