Tread carefully. A BMW 7 Series is a huge luxury car that's quite complex before you start adding hybrid power to the mix. Have you considered a BMW 530e instead? They're more popular – so finding a good used example will be easier – and, with less weight to haul around, it should be more efficient. It'll still feel like a step up in terms of refinement compared to your 218d Gran Tourer. To get the best from a PHEV, you'll need to be able to charge at home and cover mainly short journeys. Careful, though, once you discover the benefits of a PHEV, it's a slippery slope towards an electric vehicle...