If you do opt for a full length swim platform you need to pay attention to the design. Most sailboats that I have been on with full platforms across the stern end up with a corner of the frame dragging in the water
when the boat heals.
If you can fold it up that would be ideal.
Another issue with big swim platforms that are fixed and not folded can occur when running down swell. If you get pooped think about how much water will suddenly be supported by the platform or grid structure.
My boat has a platform thats too large and it does drag and although its fine for the type of sailing we are currently contemplating I wouldn't expect it to survive an ocean passage
in rough conditions.
As far as the original question is concerned. You can talk to a marine
fabricator and I am sure they will be able to look at your boat and make some suggestions. The next thing I would do is walk a few docks and look for something you like on another boat. Take a photo
of it and go from there. My grid a is 1.5 inch stainless frame with a deck
on top. It looks every bit like what you would see on a ski boat.