I’d go for a smart trouser suit, which I would expect to get plenty of other wear from.
I would dress it up with a lovely silk or lace shawl, to look a bit wedding-ey.
I got married in 2014, after living together for 38 years. I wore smart trousers and a dressy top. I have worn everything, including the shoes, many times since - on holiday, out for meals, to family parties and events.
My aim would be something classic.
Have a good root through M&S, Debenhams and House of Fraser, on line, as they often have discounts and offers. Do it now so that you can return things that don’t work.
Congratulations, have a happy day.?