You had stock 6 gears, you can get from Brompton a 8% larger chainring, a 54T vs the 50T you rode.
Yes, you can get even higher if you really wanted, there is the Schlumpf High Speed Drive with a real 27T which it steps-up by 2.5x to make a virtual 67.5T chainring so a 35% increase in your highest gear, plus a low gear 46% lower than present. Schlumpf adds weight but the HSD is the lightest.
Hands - should not be a problem with M-bars, suggest you investigate technique, you may be feeling the steering as too light and so are compensating by gripping harshly - relax. That is 99% likely your problem, and will resolve as you get used to the Brompton. However you can get Ergon grips they produce a moulded palm rest area.
All the above ideas add weight.
The weight-reducing winners are to move to a 2-speed instead of 6-speed, which lowers your highest gear, and to move to Titanium.
It strikes me the Brompton may be the wrong bike for the rider
