More or less the same problem: in the city were I live, there are a lot of cobbles roads and a lot of short steep roads.

The Brompton is miserable on cobbles and its transmission very bad in case of steep climbs and steep downhill, not enough overall gear inch, too much gear inch difference between gears.

I upgraded my Brompton with a Rohloff that solves the climbs/downhill but the problem with cobbles remain, the frame of the Brompton is also not very efficient.

The solution for me is the Moulton when I do not need to fold and want a sport riding (the one I have are lightweight and very lightweight, actually the lightest possible Moulton) or the Birdy which is very versatile, ride everywhere efficiently due to its wide tires and full suspension, much more efficient frame than the Brompton, a lot of possibilities to carry stuff with a Brompton front block + rear rack with Vaude rear pannier and folding only slightly bigger than the Brompton.