Sounds like the exposed ribs are the major problem. I just finished flooring my new hull (1652 G3). It came with the same type of exposed ribs.
FIRST, I dragged four sets of wires. I only needed two sets for my Trolling motor and forward electronics. So I thought. It wasn't but a few days and I realized that I needed a run of wire to power my forward navigation lights. Now, I have one spare set awaiting some other need.
I cut up some blue foam (sheets available at Lowes or HD) and built up enough layers to fill the gaps height-wise. Contrary to the norm, I cut the foam "logs".... loose/thinner .... in each cavity. I wanted some space for water to find its way out ....since it will eventually find its way in.
I had a 4x7 piece of thin aluminum sheet that I removed from my old hull. But, it wouldn't cover the entire width of the new, larger, hull. I went to Lowes and had them cut two pieces from a 4x8 sheet of EXTERIOR grade 1/4 inch plywood. Since I was covering it with vinyl, I used BCX grade. If you intend to cover your new decking, I'd suggest you consider carpet. My belief is that your folding chair won't slip as much on carpet. If not for that issue, I really like the vinyl.
I installed the new decking in two pieces rather than one, simply because it was easier, and I worried about some future need to get under the deck. I Have a small side-console that would make future access difficult if I had gone with a single sheet. A single sheet probably would work best in your situation, though. Lowes will cut a sheet to length for you.
Some boats have a taper. The hull is wider in the stern than near the bow. So, measure carefully and you will probably have to cut the tapered sides by yourself. Lowes' panel saw isn't designed to cut tapered edges. No big deal. You can do it with a circular saw or even a saber saw after clamping down a straight-edge.
I screwed my decking sandwich ( aluminum and plywood ) down to the ribs with stainless steel screws. BEFORE laying down the plywood, I added some bright blue tape markers on the sides of the hull, aligned with each rib. That made it easy to locate the ribs into which I screwed the plywood.
Many guys on here swear by using only aluminum for the flooring. They may all be right, but this method worked for me.
Sorry for such a long post, but I wanted to tell you how someone else had accomplished adding the flooring, in enough detail, so that there shouldn't be too many unanswered questions.
regards, richg99