In my search, I remember seeing someone who was selling tanks that would just go on with your Nursing Bra, so you could wear them under a button down or regular top & they work to keep your tummy covered when you unbutton or pull up the top layer.
They seemed pretty simple, and not worth paying someone else to do for me. So I have it a go ...
I got mine from Old Navy for $5 each.
(Sorry it's hard to see in this photo)
I tied a knot after each stitch to make it stronger.
You could do this on a machine too, I was simply too lazy to drag mine out for this little project.
The tank loop fits onto the Nursing Bra and provides you with an extra layer to keep you covered & warm !!