@OneHappyMomma - the great thing about British weddings is that they are entirely open to the imagination and enthusiasm of the participants. Being the MOG is obviously an exciting cause for celebration, and you will want to dress up - but, in the absence of any specific religious / national / cultural traditions (you have not mentioned any) you can dress as you like. Individualism rules.
And so can every other female member of the family. You do not get to choose for them - and they do not have to coordinate with your choice. Unless they are bridesmaids and the bride is - with their agreement - providing or prescribing bridesmaids outfits for them, each guest is allowed to choose how they dress for themselves.
You do not have to buy a stiff coat and skirt from an unfashionable ‘bridal’ shop. (Although a fashionable coat and skirt might be a very cool choice.)
You do not have to wear pastel colours. Or fairground pink. Unless you want to.
You do not have to wear a hat. Or a fascinator. Or feathers.
You do not have to wear a dress. Trousers are perfectly acceptable. A trouser suit or a coordinating coat and trousers is perfectly acceptable and can look extremely chic.
You do not have to order something cheap and nasty via Amazon.
You do not have to order a wrap dress from one prescribed Mumsnet source, just because you have an hourglass figure.
Brilliantly you have not left it to the week before the wedding to indulge in MN-assisted panic buying! If you have a relatively flexible budget and want to buy something relatively special - whether online or in person - you could usefully spend a few months browsing the major online stores (because they have so much available) and then swoop decisively the moment the Autumn/ Winter collections arrive. If you enjoy a bargain you could browse the same stores and find something magnificent in the end of year sales.
Or you could have something bespoke made for you, by an established dressmaker or a Savile Row outfitter. (This might be my choice.)
Or you might run into Zara or Chanel (or wherever!) on a whim and find the perfect thing when you weren’t even looking.
It’s such a fantastic opportunity to have fun and look your best. Don’t let anyone bully you into wearing something dull.