If you use a Sony FF system with 2-3 lenses and that's too heavy, then the GFX will also be too heavy.
You could downsize to a Sony APS-C system if you don't want to migrate to Fuji. Sony also makes a number of rather small and light FF lenses.
I used a Canon DSLR with L lenses for a long time, and that's about the same size as a GFX system. With Fuji you get a remarkable amount of quality for the size and weight of the kit. But the question, I think, is whether your photography will be noticeably improved compared to APS-C. I personally don't think so.
