Pepita/houndstooth would also look fantastic. Porsche started using it in the cars in 1965. BMW also used it in their Baur Cabriolet 2002's.
I recall when I did the whole sway bar buy on here that the manager of Addco had reupholstered the inserts of his early 997 with pepita after they were worn out. It really enlivened an otherwise mundane black interior, looked fantastic.
Looking at first generation Porsche seats with those inserts, it's easy to picture how it might look in an SL. While Mercedes cars generally have many strong points, their seats always lagged (in my eyes), despite the claims of superiority over everyone else in their add copy. Even in the period, many of the American companies (like Studebaker!) were making seats that had a more robust internal construction. I
hate the No Sag in our seats. I might as well be sitting on the floor, despite having totally restored mine.