The DAZ Importer now has a new tool that adds a softbody simulation to Genesis characters directly in Blender. The setup was suggested by Alessandro Padovani in this thread, using ideas by Aneesh Arts explained in https://www.youtube.com/watch?v=eggOO9CIyp4. The Blender manual for softbody animations can be found at https://docs.blender.org/manual/en/3.0/physics/soft_body/index.html.
It should be stated from the outset that I am not an expert in simulations. The softbody simulation created by this tool works quite well in most cases, provided that the animation is believable. However, if the softbody object is subject to excessive force, either due to acceleration or to collsions, the softbody objects may collapse, giving the impression of a broken breast implant. Probably not the effect you were looking for. In such cases you either have to tweak the simulation parameters or modify the animation. But in most cases the softbody simulation does work and gives plausible results.
This is work in progress and available only in the development version of the DAZ Importer. It is not part of stable version 1.6.1.
Easy Import also has an option to add softbody simulations.
Collision objects for arms and legs can be added. If you only add softbody for the chest you probably only want to add collision objects for the arms, since it is unlikely that the chest will collide with the legs.
Finally there are options to add a corrective smooth modifier to the meshes and to remove existing softbody objects.
Note that the surface deform must be unbound before any changes to the mesh is done. The Merge Geografts and the new Merge Meshes tools are aware of that, and unbind any surface deform modifiers first and rebind them again once they have finished.