What to wear to a charity ball as a size 18/20

[Heyitsmeeee]

I am going to my first ever charity ball and really struggling with what to wear. Don't want to stand out for the wrong reasons 🫣. I am plus size 18/20 and average height. Are long dresses the done thing? Or would something sparkly like this be acceptable?
Thank you

Yes you need a long dress for a ball

Thank you, I'm so out of my depth! Would something like this be ok? With nice shoes, accessories etc

Potentially depending on the material. It looks like it is potentially more of a casual material but maybe I’m wrong on that.
John Lewis has a ball gown section which should give you some inspiration
www.johnlewis.com/browse/women/womens-dresses/ball-gown/_/N-flwZln2c?chunk=4

Looks just right to me. You'd need to try it on to make sure it flatters your shape, but it probably will.
For a charity ball the gowns don't have to look designer or expensive, just festive and ball-y, which this one does. You could accessorise with a brightly coloured bag and shoes etc in the same bright colour, maybe green.

The long black dress would be fine if it’s in a summer evening fabric - silk, viscose, polyester, etc. But not velvet, which would be far too wintery.

@Heyitsmeeee I think that dress is very boring and often the back hem isn’t attractive either. The sleeves look like day wear too. Having been to balls like this, it’s a bit underwhelming. Black is fine but a bit more glamorous and not a day dress.