You can add 'helper springs', but the ride will be very rough if you don't plan on towing anything. You'll get extreme axle hop over pot holes. Pick up a spray bottle (or pour out something of the wifes that she'll never use and use that bottle), fill it with a cup of red hand soap. Start the vehicle and leave it running to build pressure and while it's running, spray down the entire air suspension system from the bags, to the lines. Look for bubbles and you'll know if the bags are the culprit, or if a line is leaking. If in fact a bag is shot and you don't want to fork over the dough to replace it (I don't blame you there), then a leaf spring suspension is the most cost efficient option. Also, Firestone makes suspension air bag systems as well. You can check out
Performance Parts Online for Cars and Trucks - Performance Center for additional options. The air bag systems might be universal, and not truck specific, good luck!