You didn't state the year of your car, so no way for me to check, but if the factory service manual says the recommended torque is 13 ft-lb, then best to use that. If you're concerned they plugs will work themselves loose, just check them every month that they are staying in tight as you first installed them. The discrepancy might be that on older engines the threads in the head become a little carbonized so at the recommended torque they aren't twisted in quite enough b/c the carbon is preventing the plug from turning freely. Suggest to take a look at the threads with a bright flashlight/mirror. Pretty sure that overtightening will end up resulting in much more work and cost for you than under-tightening with even a weekly check of the plugs until you are certain they are staying put.
I always use a torque wrench on my Corolla's plugs, which are very easy to access, a straight shot. But on my Ford's v8 I only use the torque wrench for the plugs at the front of the engine. For the harder to reach ones, requiring an angled u-joint adapter approach, I do it by feel, based on what it felt doing the easier ones, and how many degrees I had to twist them from first contact.
I always use a tiny dab of some form of anti-seize, both on my Corolla, and my Ford.