Thanks for your reply, IJustLosttheGame. The clothes came from my great aunt, who was about a 16 then, but a decent size 12 nowadays, plus one from my great grandmother.
The former is a sheer black lace shift dress, ankle length, with a silky black undershift and a black lace jacket with chiffon edgings and ties. It is very fragile.
Second, is a black bias cut silk satin 1930s gown with diamante on the shoulders and edging a plunging back, sleeveless, with a dropped false drape so the shoulder is exposed but any bingo wing disguised, and a full length flowing skirt. Very wearable and elegant, I have been told it is museum quality.
Then there is a very formal black wool dinner dress, made for a cousin's 21st about 1947. It's fitted, long very narrow sleeves, with a three tiered pencil midi skirt and a bustle with a bow. Each tier is grosgrain trimmed, and the scoop neck has a panelled section with the effect of a man's dress shirt with a slight sheen. I have worn it for formal dinners in the City.
I am keeping a purple taffeta ball skirt that I had cut down from a 1950s dress where the bodice was ruined by a perished hot water bottle, because it is incredibly useful for modern formal wear, with a silky T shirt or a dressy cashmere top in winter.
And I have a late 1950s cocktail dress, also black, with a fitted beaded bodice, sleeveless, crew neck, and a circular three layer chiffon shirt in black and flesh, that I was given. It fits a (modern) size 8-10 and is below the knee.
I am a narrow hipped hourglass in a 12, but by the standards of the day, I would be a 14-16! And they are the right length for someone reasonably proportioned of 5' 4". I will be doing some pictures, but probably not today. Would be very interested in any thoughts you have! And thank you again.