Need a little more info on the boat to really answer that question.

What size boat? Is it a 17 -18 foot open fiishing boat, or a bigger boat with a cabin? Is it stored inside most of the time?

Yes Marine Plywood is the usual choice for a long lasting floor. You may want to looking into alternative materials that may be available today, such as plastic or figerglass. Something that won't rot out over time like wood does. I don't know what may be available. Stop into a repair shop and ask, and do some Internet research.