You could try swapping the plugs on the back of the switches so the left one controls the right side and the right side controls the left. If the problem stays in the one switch, chances are you need a new switch.
I would hate for you to buy the switch and find out that is not the problem. It'* pretty easy to pull the switches out and swap the plugs. If you do end up replacing them you could also compare that price against your local GM dealer. They should be able to order the part for you, although I think I paid right around $60 a piece when I replaced both of mine because a couple of the lights were burnt out. I know... I'm picky.
One of your wires has been burnt at the contacts in the seat pad. You have to peel back the leather to see the contact points going to the heated pads. There are two at the front of the bottom seat plus one at the rear bottom seat that are usually the culperts. Should be a write up on it up here some where if you use the search for the fix.