I don't know about upton, but I bought one from adagio that met those
criteria some years ago. I see they have an updated version, so I
don't know if they've made changes on the inside, but mine is metal.
It works pretty well still, though the temperature gauge is (perhaps
necessarily) not real specific, so you just have to play around with
it to see what temperature you like. At the time, that was the only
temperature-variable kettle I could find.