Answer depends on many factors....try and cruise in areas of calmer waters....mid ship cabins help somewhat...At the end of the day if you suffer from sea sickness you are still likely to feel sick no matter the size.
I get travel sick on a rowing boat on a lake but have been on 5 cruises and been fine on each one. on the larger ships there is very little motion so im sure you will be fin.
May I suggest either stugeron tablets or wristbands, they both work for m.
Most of the cruise ship are fully stabalized, therefore ther is very little movement in calmer water, however a quick visit to the doctor on board who will give you a injection cures all sicknes.
I get sick on small boats, cars, coaches, planes, trains...even fairgrounds! I have been on lots of cruises and have only once been sea sick, take the sea sickness pills and you'll be fin.