Making a PVC model is a good idea. You could clamp PVC or wood stanchions to the existing rail's mounting points.
Perhaps your new rail could extend, continuously aft along the side or top edge of the house. I don't have the sense of how high the new rail wants to be, or how low the side deck is behind the sheer.
When shopping for our trawler, we eliminated some lovely boats that had narrow side decks and poor handrails.