60th birthday dinner - where to shop?

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Any ideas from you wise women for places to look for a birthday outfit? Size 18, (a good 18 M&S level), no dresses or skirts. Thinking some kind of statement shirt or maybe a fancy jacket/blazer. Not a fan of the floaty.
Any ideas for shops (London) or websites? Happy to spend up to a couple of hundred if it's something I'll use for other parties.

I got lost down another the rabbit hole of another post- suit for a wedding or something. Lots of beautiful separates on there that you could wear for a birthday dinner.

Yes I saw that after I'd posted. Thanks. Looks helpful! Still after ideas for a fancy jacket - the kimonos look nice but I feel structure is better.

Have you tried River Island? I had an amazing statement blazer from there last summer it was lovely quality.

www.riverisland.com/p/red-lace-blazer-756574

www.riverisland.com/p/plus-orange-cape-blazer-760014

www.riverisland.com/p/plus-pink-dogtooth-boucle-blazer-759499

www.riverisland.com/p/plus-coral-double-breasted-blazer-770878