Galapagos Islands on the Isabela II
The best options if you get seasick is a larger, more stable boat, or in a wide catamaran. You will want a cabin on a lower deck, mid-ship.
The Galapagos limits the number of people on a boat to 100 maximum.
Here are some of the larger boats we recommend:
You may also want to consider an Island Hopping Galapagos Tour.