My partner and I are getting married in a few months and this is roughly the kind of dress she is looking at. It will be somewhat casual obviously, small family affair.

https://encore-paris.com/products/annabelle-maxi-dress

It won't be exactly this as we do not live in the warmest climate, but was looking for ideas of what I might wear that would match this type of thing, mostly in terms of how formal/casual to be.

I was thinking suit pants, shirt and tweed waistcoat/vest . Not entirely sure what colours outside of likely white shirt and a pocket square to match floral design colours.

Maybe something along the lines of this but correctly colour co-ordinated. Was thinking no tie - A bit rough and ready suits me, it wouldn't be out of place. Alternatively might look at an ascot, never worn one before so no idea if it'd work.

Ideas? Opinions?