Is it in the uk ? Will it be chilly for some of it , cold church .
I think as it is a block colour you could go for some pattern . Anything that has a bit of pink in it . I love patterns / florals but know not everyone's cup of tea .
As the dress is also straight you could get something slightly more floaty . Even kimono / duster coat style if that is something you would be comfortable in .
One hundred stars is the default for kimonos / but they may not have anything you like as very distinct style . I personally don't like the ones with belts as I think they do look like dressing gowns .
When do you have to buy / when is the wedding as I think shops are bringing out more of the spring clothing . I always find Zara has a great selection of jackets . So you could keep checking on new arrivals .
If you are wanting something slightly warmer , you may be lucky to find something online in the sales . Usually velvet though . Warehouse usually has a good selection.
Depending on budget , Lisou and Nancy Mac also have beautiful jackets but quite pricey .
If you do find a style you like , but it is too pricey you could also try Vinted , although you may have to scroll through a lot . Put in the filter new / new with tags .
Good luck .