Look through several offers’ wordings. Most are available online to download. They are pretty much in Janet and John language, despite what you might read on these pages.
It might be cheaper to buy an annual (multi-trip) policy, than one single (limited period) policy.
Also, don’t forget to incept (start) the cover on the day you make the first significant payment towards your holiday. For example, when you buy your ferry ticket. Don’t elect to start it on the day you leave. Why? If you fall ill or injure yourself BEFORE the policy starts, you have no cover for any costs you have incurred. The difference in premium will, in all probability, be pretty small.