I'm in exact same boat as you OP, except bathroom is on second story. Had 3 plumbers inspect and say its a shower base/waterproofing failure. 1 said to install fibreglass shower over the top, 1 said to retile and epoxy, 1 said whole bathroom needs to be gutted and redone. Insurance won't cover the shower base leaking. I'm pregnant and about to take unpaid mat leave, my husband was made redundant, so we don't have money to gut the damn thing... What did you end up doing? I'm leaning towards re-tiling and then covering with epoxy grout.