Hello,
I like the current transformer idea too.
I forgot to mention one detail in my last post however. That is, if the 47 ohm resistor is raised that relaxes the lower Ohmic requirement of the resistor R4, so R4 can be raised.
For example, if with 47 ohms (which is close to 50 ohms) if a 20k resistor is required for R4, then with 47 ohms changed to 100 ohms that means roughly a 40k resistor for R4 would be required. That reduces the power requirement for R4 to 1.3 watts so a 2 watt resistor might be ok. Following that line of thought, raising the 47 ohm to 200 ohms means roughly an 80k resistor for R4 might work, with the power requirement being 0.65 watts. Similarly, a 400 ohm resistor and 160k resistor for R4 brings us down to around 0.3 watts and maybe a little higher like a 500 ohm resistor and 200k for R4 brings the power requirement down to 0.27 watts so a 1/2 watt resistor would work.
This should be tested carefully however because the accuracy is always in question.