Are there any “slow” boats between Heraklion and Santorini for someone that is prone to sea sickness?
If the sea is rough then slow is not better, it’s longer. Anyway if you take a dramamine or even half that usually works. Its not worth worrying about because if even 5% of the people who were afraid of getting seasick on a Greek ferry actually got seasick on a Greek ferry there would be long lines outside the toilets. These ships are huge, modern and are more like flying than being on the sea.