I am rubbish at numbers, or understanding explanations about numbers.
So really need help with my bra size.
Personally I would go to a place like Bravissimo and get the expert ladies there to fit you.
I have found over the years that shops are not the same standard size at all. https://www.upliftedlingerie.co.uk/bras/42g-bra
I was measured as a 30G in Bravissimo, and a 32E in Marks and Sparks, all in the same week.
Bravissimo nail it for me, loads of lovely styles as well for the fuller lady.