I've been messing around with Blender for a few years, but I'm not a pro, so take this with a grain of salt.
As nice as the model is, it's not well equipped for inflation deformation. I like to make a bunch of different shape keys on the undergarments and then apply the transformations. This has too much clothing which is bound to the model. I guess I could pull it off and see how the mesh looks, but it's really best used as intended: for animation, not resculpting.