Piggyback input power from supply power on SSR?
You cannot use the 240V to supply the control coil of the relay as you show in the picture. To me is difficult to understand really what are your specs, the driving coil changes with the power rating of the relay. Can you provide more specs?

To get a DC voltage to supply the coil one of the cheapest solution is similar to RC voltage divider https://www.microchip.com/forums/m/tm.aspx?m=841330&amp;p=2