Just some thoughts that might be of use....
I'm surprised it handles poorly compared to old Falcons. All small Fords are generally good handlers, and that generation of Focus was no exception. It's not on original tyres, is it by any chance?
To be honest, I got a Whiteline sway bar in an LV (2010 model) and could barely notice a difference, which wasn't the case with a VW group car I had later. It also means sacrificing the
IRS in the Focus.
What variant is it? CL or LX, perhaps? THe Zetec model was the sportier one in that generation, so if you could get the larger wheels and/or springs etc from one of those, it would be an improved handler and everything would fit. Maybe better tyre options as well.