measuring electricity on a shared circuit
You're looking for a home energy meter. These are available with a clamp-on current meter and wireless remote display.

There are several details missing from your question.


What country you are in.
Where the fuseboard is. If you are sharing a fuseboard with the business than the situation becomes more difficult as you would have to monitor each of the lighting, socket, cooker, water heater, etc., circuits individually. If you have a fuseboard for your flat then you just have to monitor the incoming cable.