The docs you point out lists all the available types (depending on argument type), and as you see, GTK_TYPE_SWITCH is indeed supported. Just use it for the last argument.
As for using a GType in the Python binding, this was already explained to you here: GIMP3/Python3 Sliders instead of spinners? - #2 by JimDee2
It’s the same thing here, except that it will be Gtk.Switch.__gtype__ in this case.