I don't remember all the details but some years ago we met another Santorin owner in the Med who had extended the aft berth with a "foot-well" into the aft locker area. I recall he was a cabinet maker and it was a good looking "Amel-like" job that did not seem to compromise anything structural and retained the water-tight aft lazarette, albeit making that a bit smaller.
We modified ours at one point with a filler piece of plywood and a couple of supports that gave us athwartship sleeping. That gave a very long berth that was comfy in a roll. I had engineered it to be changeable at will so now we have three possible layouts: 1. Two separate berths; 2. one single to starboard and a double to port; and 3. an extra long, extra wide athwartship "king" size berth.
Lotsa ways to skin a cat.
Craig Briggs SN68 Sangaris, Tropic Isle Harbor, FL