first, start off by deleting your second cat at a muffler shop. just try to ask around and find one which uses stainless steel or is reputable for good welding. it will be cheap, and will free up some restriction but your car will not be significantly louder.
because of the design of this exhaust system, a full cat-back is not offered, but I would not recommend one anyways because the stock exhaust system on these cars is already quite well designed. you are much more likely to see axle-back setups (muffler only) which is what I suggest for you, but with the second cat delete should be optimal.
alternatively, you can remove your muffler and have the shop weld in two resonators right behind where your exhaust tips are - that would sound excellent but I honestly can't suggest removing your stock exhaust system because the large bubble shape helps extract air out from underneath your car.
honestly, if you want a good sound that will be heard without being annoying or raucous, I would find someone such as Corksport to make catless headers for your car with one resonator added in somewhere, and the rest of the exhaust stock. then get an ECU tune from orange virus. you will get a very healthy power gain and the sound will be amazing.
good luck and let us know with what you end up doing.