Been there, we had to abandon a deal with a SUV because of the car sickness.
I had a loaner 520D, non-M and it was nice and smooooth
Drove also several times G20 330e M-sport, which has very nice suspension, very precise and good, but not as comfortable as G30. Seems like the principal hasn't changed since previous generations: The smaller the car, the bumpier the ride.
Note, too soft ride can also cause car sickness! At the end of the day, it's how your wife feels it, you'll just need to go together to drive them and the 5 is a good starting point.