I would go for a really big bulky black (or black floral) necklace, something bulky to give the dress some texture and contrasting colour. Can I suggest the charity shops - I've bought some amazing jewellery from charity shops. Also, you could try making your own. I had my makeup done at the weekend and the make up lady had on a black dress and the most amazing black feather stole
black / peacock feather stole cape shrug 40s / wedding - just to give you an idea - again, charity shops - some fantastic bits - you could even make your own if you're that way inclined. I can also recommend Primani! You can get some really nice bits and at not too much cost. 