If you are driving a MINI or a BMW, you know how stiff the ride can be. One option would be to replace the tires with non-run-flat tires. While you may not have a spare tire, there are options for that as well. Roadside assistance is available on the new cars and you could get a spare to put in the trunk. The other option is a Continental ContiComfortKit.
Take a look at the new Yokohama AVID ENVigor if you need longer wear and an all-season tire. It has a low rolling resistance rubber compound that will work in the cold weather and they are still a good handling tire. You will have a big advantage over the much heavier run-flat tires that came on the car. I have driven these tires and they are very quiet, smooth riding tires.
So if you want to make a change to improve ride quality, an easy fix is replacing the run-flat tires.