I used different things at different times.
At first, while I was feeling so sick, I couldn't stand anything tied around my waist. So all the mei tais went away, and I broke out the ring sling again, or back wrapped with a tibetan tie for longer trips.
Then, when I could stand things around my waist again, I got a toddler sized Olives & Applesauce full buckle, that I buckled below the bump. That worked for a long while.
The last month I didn't wear much at all, because I was feeling pretty tired, and if I stood up for too long, or carried much weight, it really put a strain on the vaginal floor muscles. You know how they tell you to do your kegels? Turns out it matters. Who knew? :S