I can't tell from your profile where you are located. My suggestion below would only work for you if there are marine craftsmen located near you.
Last Winter I replaced the part of my cabin sole that had warped. It may be too expensive to scale up to as much as you need, but you can decide that for yourself. I bought some 1/4" teak and holly remnants from a local shop at minor discount, epoxied them to 3/4" marine plywood, cut the pieces to size, and sealed the bottom and edges with epoxy. The two pieces were each about 2 sq feet. This approach was a lot less expensive for me than buying a half (4'x4') T&H sheet and another of marine plywood on the web, even with the extra cost of using a flexible epoxy like Waste Marine's G/Flex 650
so that it flexes when the wood flexes.