Thank you both... yes, demoralising...
So here's what I bought:
Juna Balconette Bra, Ivory, 28D1£23.00
Paige Italian Lace Half Cup Bra (A-DD), Red, 30C1£24.00
Marvel Underwired Side Panel Bra, Nude, 30D1£30.00
Patsy Underwired Padded Half Cup Bra, Black, 30D1£31.00
Microfiber T-shirt Bra, Black, 30C1£31.00
Patsy Underwired Padded Half Cup Bra, Ink, 30D1£31.00
Patsy Underwired Plunge Balcony Bra, Ink, 30D1£31.00
Beau Underwired Plunge Bra, Lollipop, 30D1£32.00
Lola Scallop Lace Padded Plunge Bra, Neon Pink, 30D1£34.00
**Icon Perfect Push Up Bra, Bare 20N, 30C1£35.00
Stella Mesh Balconette Bra, Blush Pink, 30D1£42.00
Embrace Lace Contour Bra, Black, 30D1£43.00
Merci Memory Foam T-Shirt Bra, Black, 30C1£47.00
Merci Memory Foam T-Shirt Bra, White, 30C1£47.00
Merci Memory Foam T-Shirt Bra, White, 30D1£47.00
It's almost impossible to work out how names match to actual bras - the one that fits me best is a white Chantelle one, 30D, that I can't see here (it'll have another name).
Most of them gape at the top. Some manage both to gape and to squash. I don't know! I feel like I'm a hopeless case...