You haven't made it too complicated, but your diagrams suck.
You're correct. I should have made my A, B, & M boxes a different colour from the wire.
I did have a power source - battery, there is a symbol on the left.
The load would have been in A, B, or M - resistor, or something.
* an electronically controlled switch or relay - probably implemented as a transistor or MOSFET. The actual circuits will tend to be simpler if its between the load and the -ve side of the power source.
I need to study how these work, to understand that.
* a current sensor - probably implemented as a low value resistor with the voltage drop across it amplified. Again the circuit will be a lot simpler if one end of the shunt directly connects to the -ve side of the power source.
I don't know how to amplify the voltage across it, or what a shunt is.
* a pushbutton switch. Unless there is a specific requirement otherwise, it gives us more options if both its terminals go to the control block.
Sorry, did not know there was a specific push button switch symbol.
* an as yet unspecified control block that takes the signals from the current sensor and the pushbutton switch and provides an output to the electronic switch. It needs power and ground connections to do its job, but if standby current is a problem, you may choose to let the button supply its initial power then take its operating power from after the electronic switch which would then need to be on the high side of the load.
Yes, ideally I do not want current to be used in standby mode.
I've updated my diagram, hope it is a bit clearer.