There are a ton of aftermarket suspensions for sale (Roush, Ford Racing, Saleen, Steeda, BMR...) find one that looks like something you would be interested in. I have the Roush kit and I am happy with it. If you have 17" wheels, then getting a set of 18" wheels with lower profile tires would tighten it up a little too. Convertibles have a lot more body flex than coupes so a strut tower brace could help too. If you don't have a lot of money to spend you could just do springs to start to lower your center of gravity.