I know you want a unified look - but - just for something more to think about
I hate those full size bedspreads/comforters that go to the floor when we stop at a motel. They are heavy and uncomfortable to me. (But that is my opinion on that that.)
How about making a quilted tailored bedskirt with the mariners design - You could make them so they tuck in between the mattresses
Then make the quilt/spread so that it hangs about three inches below the top mattress.
Then have a set of pillows that are always in the pillow shams to make it look "complete" - that you toss off the bed at night. Or you could get - or make - a body type pillow that could go across the bed.
You could still get a lot of the design elements you mentioned in the "set" instead of one big unit.
I prefer a "unified" look - such as the blocks from Jinny Beyer's Moonglow quilt - the blocks are varied, but have a common theme.
Is this something you plan to sleep under? Or is it mostly for show?