Aquaclears worked great for a decade or more before they came out with "biomax", so yes, you can run double sponges.
You don't need carbon. All it does is remove color from the water (caused by lots of driftwood), remove meds, and remove odor (if you tank smells, running carbon is the least of your concerns).
What filter are you curently running? If it is a whisper or some other type of hang on back, just remove the media (rinse in dechlorinated water while you have it out) and sandwich it between the sponges on your new aquaclear. The exsisting media will continue to act as biofiltration, and the bacteria will quickly (couple weeks) colonize the new filter media.