I think your challenge is that you are combining two quite different requirements - the Brompton will be superb about town but sub-optimal in the countryside, and especially on any serious hills.
If your budget is suitably generous you could look at a Birdy folding bike.
You could (whether Brompton or Birdy) consider an electric option. I have no experience with the electric versions of either but imagine it would resolve the uphill side of the hills challenge quite satisfactorily … not so sure about the downhill side mind …