Shapewear by what you want smoothed or solved. Every page gives a verdict first, then the fit rule, then the size. Some say no; those are the pages that make the rest believable.
Shapewear bodysuit for a large bustYes, with your own bra. The built-in bra has no compression on the bust and gives light support only; a fuller bust wants a proper bra underneath, straps inside the bodysuit's. The waist panel does the smoothing.
Shapewear that doesn't roll down when you sitA bodysuit is the cut that does not roll, because the straps hold the waist from above. The adjustment is the straps: set them for your torso length, and if they pull at their longest, the size is one band too small.
Shapewear with no visible panty lineYes. A panty line is an edge pressing through fabric. The thong has no edge across the seat, and the bodysuit's edges are bonded, not stitched, so they lie flat. Match the shade to the dress and set the straps.