Ankle boots aren't right for an evening Christmas do, although they would be ok for a day do.
I would get some low-mid heel black suede or black patent courts, (pointed or almond toe, try M&S), black tights (make sure you get 60+ denier, preferably 80) and then I would probably put a mid-length necklace with that. I think the dress may need a necklace although agree with brakespeare that it might look just as good without. If you do get a necklace, the length has to be just right though - it should sit just above your bust - not so long to be dangling between the girls :) and not so short that it interferes with the neckline. I would probably choose a necklace that's quite chunky but not bejewelled. Definitely nothing fine-chained. Possibly high gloss in jewel colours. Then I would reflect that with toning clutch bag, in either a metallic colour (eg pewter) or a jewel colour. It should be quite a large clutch, not a small one, as it puts the dress etc in proportion.