I don't envy your dilemma.
Not fond of the rose gold jacket over the dress. Maybe scrunching would help. Are you looking to make a fashion statement regardless of the tone others set? What tone will be set? A wedding can be a pretty different place to be statementy than elsewhere. Depends how you feel about it.
I like the line and depth of color of the black jacket because it reduces some if the pale-and-soft if the dress, neither of which attributes seem as flattering in you as what you would normally wear. The jacket also has a graceful line that doesn't fight the the dress and reads dressy with the dress. It's not a bad option. But unless the jacket is from a fabric you would feel good in at a wedding (in other words, not like you couldn't find anything else so grabbed the jacket from your black business suit), I would keep looking.
While you're looking, favor some depth in a color or neutral, rather than more pale tones, I would think. And structure. Graceful structure, as in the black jacket, would echo the dress. Straighter structure offset the softness and might be more to your liking.
If it were me I would probably wear a dark but rich color (plum?) or neutral in a substantial cashmere it cashmere-like wrap that could be worn tied around your neck with street clothes either on this trip or back home on colder days. I have a black one like that that I travel with and it works for everything from airplane blanket to scarf with jeans to topper solution for dressy events. But I get that you don't care for the shawl effect.
A leather, sequined-knit, or metallicized fabric in a jacket line and construction that looks hip to you but has more refinement than toughness and doesn't look accidental with the dress, as I think the rosegold jacket sort of does, might be a place to look.
Being a bridesmaid is rarely easy!
