I have a black tie dinner coming up in about a month's time. These are about as common as hens' teeth in my social schedule, so I am looking forward it!
I have a few cocktail/evening dresses in my wardrobe, but I think they might be a tiny bit on the tight side now. 
Would any of you wise ladies like to suggest something?
I am 37, 5'7 and have fair colouring. My colours are pink, green, red, brown, ocean blue or cream/neutral. I quite fancy a colour that could work well for winter or summer, as ideally I would like to get a second use out of it if possible. Budget maybe up to £150 max.
I have a small waist and bust, so prom style dresses look great on me (or am I too old for them?), but strapless doesn't really work! My legs are quite long so knee-length is about right for me.