Solar Wind Speed, Magnetic Field Strength and UV Output can also be used. And you are correct that sunspot numbers are a very crude way to determine solar activity. Made even more inaccurate with the fact that they are counting more sunspots in modern times due to enhanced optics. If you look at some sunspot charts for the people who try to bias for the modern extra sensitive measurements, this has been a very weak solar maximum. In fact one of the weakest in modern times.
