Cracked and sagging floor

I'm preparing to build and install subframe connectors. While under my car today, I noticed the drivers side floor around the inner front seat stud is cracked (the one toward the back). The floor was sagging in that area also.

I jacked up the sagging area and hammered it back into shape. Still need to weld up the crack. Has anyone made supports from subframe connectors to where the seat mounts? Not sure the best way to get floor supported to keep it from sagging again.