Is it actually coil bound and sitting on the bump stops ?
Your description makes me think it's your dampers, not the springs. I fitting heavy duty adjustable dampers to my Jimny, it made a massive difference when fully loaded, the soft feel went away. It now almost feels too hard without a load on the back.
Are your dampers good?
Yokohama Geolanders, Sony head unit, NAUTILUS Air Horn, DRL conversion, Rear cargo space, Elvis Bobblehead, transfer Guard, Indian hanging Elephant, Koni Heavy track dampers, Custom SS exhaust, Voodoo Doll, Adventure Rack with LED ight bar, vintage ERIBA caravan usually attached (yes it's slow)
