Don't add another relay, that will just make your fuel pump circuit less reliable. Instead, just wire the switch in series with the ground lead for the existing fuse pump relay inside the Power Distribution Center on the passenger-side fenderwell. The computer grounds that lead when it energizes the relay so you can just insert a simple on-off switch into that circuit.
Make sure the switch you use is HIGH QUALITY and properly spliced in with adequate wiring protection. This is one circuit you don't want to be any less reliable.
And if this is meant to be an antitheft device, car thieves don't always even try to start the engine. My TJ was stolen two years ago and the thieving bastards just dragged it out of its parking space and onto a flatbed towtruck. They never even tried to start it.