...Missing thermometer any recommendations
That WSM looks too old to have come with a thermometer originally. Can you provide a picture of the area where it's missing?
For a "stock" appearance get a Weber thermometer and bezel, part # 63028 and 63027 and drill a hole. There are higher quality gauges out there (such as from TelTru) but usually not for smokers. At any rate, a Weber thermometer will be plenty accurate enough, for a while. And then after a couple years you toss it and buy another. They're cheap.
But what you really want is a Thermoworks Smoke or at least a Maverick 732 or 733. Dual probes and remote readings. And of course you can use them for other grills. The Thermoworks Smoke will be more accurate than the Maverick, in my experience.