You can simply add a new bone to move the attachments around as needed. That is the normal way of doing it in Spine. In Spine Professional you could use mesh deform keys to move an attachment around, but using a bone is generally better because it's just animating the bone's X and Y, while deform keys are animating the X and Y for every mesh vertex. It would probably not make a difference with a mesh that has a low number of vertices (say 3-5, maybe <10) but if your mesh has 100+ vertices the overhead for animating so many vertices can add up. Using mesh deform keys can also bloat the size of your animation data, as each key stores all the vertices for the entire mesh (not exactly what happens, but a close enough description).
Also note that you can add a new bone to manipulate an attachment not just with translation but with rotation, scale, and shear. Using scale and shear can give you some nice squishy-ness without needing to use meshes.