Want something a little raspier but not louder? Get a header. The best money you can ever spend on your exhaust.
Buying a muffler for a Vios will get you a fruitier sounding exhaust and very little to no gain in power. A good header will make it sound deeper and throatier, and will net you between 5-10 horsepower in the midrange, right where you need it.
Speedlab makes headers for the Vios. It's not on their product page, anymore, but you can ask about it.