You will feel motion on all ships if the seas are bad. Crystal ships are still relatively small compared to the giants appearing today. There is no totally smooth cruise; that is, it may be smooth one week and rough the next. I think your best bet would be an inland passage Alaska cruise that sails from Vancouver or Seattle. As you don't head all the way to Seward, you spend very little time in open waters.
"The test of a first rate intelligence is the ability to hold two opposed ideas in the mind at the same time and still retain the ability to function."
F Scott Fitzgerald
Silversea Silver Explorer (23nts) - Kangerlussuaq, Greenland - Nome, Alaska - Aug 14
Seven Seas Voyager (30nts) - Dubai - Cape Town - Nov 14