Personally at the rough animation stage where I use onion skin, I make each body part a different colored silhouette with no shading, so I can focus on the big movement, then quit using onion skin and just flip frames once I start working on the details in final color.
This tutorial uses similar process for a visual example. Though I use filled shapes instead of lines, because I have a tendency to erase and redraw the lines to make them pixel perfect, and during rough animation that’s a waste of time.
This is basically a change in process to be more compatible with the tools, but this process also has other benefits besides onion skin, like being easier to see the motion of one part without having to solo the layer. Hope that helps.