I'd wear a skinny belt rather than a thick belt. Would wear a skinny belt in bright yellow, coral, red, cobalt blue, gold or tan depending on the occasion. The dress is that plain it is actually very versatile - could be worn with black tights and blazer for work, bare legs and heels for night out or slouchy scarf, tights and flat boots for casual day look.
It would look good with black footless tights ballet pumps no accessories though.I don't like 'snazzy' scarves with black always looks a bit old lady at a do.Unforgiving shape though but stunning if tall and skinny
I'm not in love with the dress personally - too dull in colour and style and I just don't see how it would flatter anyone, but I would go for a wide belt myself - I don't think they're over yet, seen a lot around in London with dresses and jumpsuits.