Do you need galvanic isolation in your system, and where do you need the galvanic isolation barrier to be?
Many mains energy meter consumer-type appliances don't use any galvanic isolation at all, they don't need to, and they use stuff like transformerless power supplies and the local DC ground (or positive rail) defined as the hot AC line, but if you want to do things like plug the system into a PC or other devices or have it exposed for human contact with the electronics then you will need to isolate it. You just use a voltage divider and a differential amplifier, energy-metering IC etc. These sorts of chips, the Analog Devices ones, Cirrus ones etc typically use something like an SPI interface to a microcontroller (pulse output sometimes) and you can put isolation in that link, using good old optocouplers or iCoupler ICs etc.
You can use a potential transformer (or just an ordinary step-down transformer which is the cheap alternative to a "real" instrumentation-style potential transformer), and this is potentially the "easy" approach since you don't have to worry about any electronics on the non-isolated side, any design or PCB layout creepage distance or anything like that.
There are some chips from Silicon Labs that do line power metering + galvanic isolation in a single IC.