Attending a black tie wedding (ultra high net worth)

Hi all,

I'm attending a black tie wedding in November in New York City. The bride's family is ultra high net worth and hosting the wedding.

I'm a plus size woman (240 lbs, 5'3") and generally haven't dressed myself well in life due to my size and lack of clothing options in my size.

I'm attending this wedding and have no idea where to start in terms of finding a plus size black tie dress (that's also not super cheap looking on my body). I'd prefer to hide my arms as they are a major insecurity of mine.

Can anyone recommend what I should do here? Should I get something off the rack and tailor it? Any websites or brands you would recommend?

Thank you in advance!