I'm going to a black tie do next month (first one I've been to in years!) and I've found a dress:
www.johnlewis.com/john-lewis-sleeveless-jersey-dress-navy/p827320?colour=Navy
and now I need to find shoes and some kind of coat (I will have a short walk from the hotel we're staying in to the venue, although if it's raining we'll be getting a taxi!)
Shoe-wise I can't manage ridiculously high heels as I'm massively out of practice. Coat-wise I have absolutely no idea what will work. Any ideas/reasonably priced suggestions will be very gratefully received!