No point in buying the standard cat because they so expensive, it's actually cheaper to get a sports cat instead unless you can pick up a second hand one.
Exhaust options, could have a custom made one by Pro Speed, Longlife, Powerflow etc... buy an aftermarket one made by magnex for example or do what a few people have done is pick up a second hand exhaust system off the
Ibiza Mk3 20vT and that will fit straight onto the Mk2.
If you don't want a loud exhaust or worried about the sound best bet is to go for a custom built one because you can pick the sound you want or finding a 20vT exhaust.