Nice boat.
My suggestion would be an additional custom Bimini top for the aft seating area.
Any canvas shop could create that new frame and canvas section.
My suggestion would be to have the frame designed so that it folds out of the way, such as against the existing arch.
It is possible that some of the frame could be attached to the existing rear stainless frame hoop, w/ an additional hinge hoop frame section towards the rear, pivoting off that existing frame.
https://srweb-assets-prod-a.s3.amazonaws.com/boat-pages/2019-sdx-270-ob/slider_images/6-2018-4556-2.jpg