Our house has a fully enclosed sunporch in front with an existing ceramic tile floor. There are several existing layers of floor underneath but we can't see what its all ultimately resting upon. One thing for sure, there is no basement below and its not a crawl space either. We want to apply insulation over it, then have a new plywood floor built overtop so we can put down marmoleum flooring which is a natural product that is glued down in sheets. Is this feasible and if so, what products should we use?

 

I don't think this is feasible - I'd rip everything out, insulate between floor joists and start over.

 

It sounds like you want to add ANOTHER floor over the current thousand layers that you already have. Like Mitch says, rip out the old flooring and then install insulation and new flooring. There will be joist of some sort that you can install your new flooring onto. If there aren't joist, then there will be a concrete pad.