Magic garment for a pregnant lady

[Mumswang]

ive got a friends hennight in a couple of weeks

There is a dress code. To comply I will be wearing a black 'grecian' style maxi dress

It fine from the front but the back is all lumps and bumps, I need some kind of smoothing scaffolding to support my enormous bosom but not give me a tyre where my brastrap goes across the back and my double hips are a problem too

Help