Most costume/fashion designs are drawn using a stylised sketch or 'croqui'
Some very basic templates for figure shapes are provided here. As these were quickly drawn in Inkscape, they might not be as poseable as those drawn in other tools.
The use of human modelling tool such as Poser (proporiatery) or MakeHuman("free") is strongly suggested to create a base figure onto which a sketch design can be traced.
There doesn't on a cursory web search seem to be a 2D vector tool for quickly creating croqui poses at present.
Example Croqui poses: (scaled for display, Click on them for Download if you want full-res)
Poses for Female design on masculine form (for Drag/Crossdresser) etc,: