This works but decora switches usually have both screw terminals and push-in terminals.

If you wanted to get rid of the pigtail you could put 1 of the doubled up wires on the line screw terminal, and the other into the line push-in terminal. Then connect the single load wire to either of the load terminals.

Most likely the dip tube.

Also, I havent seen anyone ask if you have a mixing valve on the outlet pipe. Here in canada they're code and often the source of fluctuating or lukewarm temperatures. Replacing them is easy if you buy the exact same model.