Re: Non wood interior sole alternative
The real problem is that plywood is actually an incredibly good material for boat building. It is relatively light, and very stiff for its thickness. Unless you are willing to take a pretty significant weight penalty your options are pretty much plywood, carbon fiber foam sheets, and webbed metal grating.
Most engineered woods don't have the stiffness you would need, and things like starboard are both significantly heavier and not stiff enough.