Consider the double breasted vest. There are a variety of styles for a man's vest but we generally see just the single breasted (the upper right panel in the illustration). Once in a rare while that single breasted model will have notched lapels in a more conservative version of the vest at the lower right, but that's usually as adventuresome as contemporary clothing gets.
Well I'm here to to talk up the double breasted shawl collar model (center left) as a change of pace for a dark single breasted city suit. The double breasted vest is a bit harder to make and fit and I assume those are the reasons it fell out of favor on the ready to wear racks. That rarity makes it a nice choice for a bespoke change of pace.
Consider that a DB vest is not flashy like slanted pockets, which have run their course as London's version of a "my suit is bespoke" symbol now that they are found on off the peg garments. The owner of a DB vested suit can just leave the vest hanging at home and wear the jacket and trousers when the occasion calls for discretion. The rest of the time he's got something interesting to wear to a cocktail party. And that's a good thing.