Depends a lot on how much headroom you can afford to give up.
Carpet (bad move in a boat My opinion) linoleum ar a similar floor covering. I have seen some linoleum type floors on boats that looked really nice. Advantage there is that it's normally a quick and durable floor with easy installation (normally) and can easily handle a flexible sole. Disavantage is that it's hard to tell by looking what will work on a boat. some floor coverings have a greyish backing which is just lightly pressed paper with some binder in it, which will absorb moisture and swell up like a cardboard box. -REAL- linoleum, and a few other coverings don't mind getting wet at all.
If you'd prefer wood, Many of the home improvement stores carry tongue and groove teak flooring,(among others) in thicknesses ranging from 3/8 to 3/4 inch. A local Menards carries (did carry anyway) teak in 5/8 for $39 a box, which was enough to do the sole in my Triton with a bit left over. (being 5'6 I could afford to give up 3/4 inch out of 6ft headroom though)
Another option for a wood sole, if headroom is critical and the existing sole is stiff enough to allow it, is to obtain some thick veneer and cover the floor with that. That can be ripped into strips and applied like planks if you'd prefer. If the sole is too flexible, you'll have to go with material thick enough to be self supporting, or flexible enough to take it.
Ken.