I don’t believe Grafana allows you to overlay different types of panels 
You could set the two up underneath other, but the left/right doesn’t match up due to axis labels & different margins etc.
The only other option I can think of is to use a secondary Y axis on the standard graph panel with 0 & 1 as the values, and give the switch item series a background colour and enable fill/shading, and enable stepped mode on these series so that you get the on/off effect.
As soon as I reconfigure MQTT so I’m getting some temperature sensor values, I may give that a try if you’ve not got round to it yet.