Congrats, Bren! I'm also getting married soon, but I plan on wearing a kilt. I have lower waisted tartan trousers and have paired them with a tweed sports coat. If you're leaning toward trews for an evening wedding, however, then I agree with figheadair that black tie formal wear would work nicely.
What jacket you wear will depend a bit on what type of trews you have (or will get). The high-waist, fishtail-back variety can look quite smart with a short waisted coatee (i.e., Prince Charlie) or a mess jacket. If they are more like tartan trousers cut at your jeans-waist, then a high-waist jacket won't work—mind the gap! In that case, a Saxon dinner jacket would be a better choice. Below are a couple pics culled from Google of what looks good to my eye.
From Scotsweb:

Sir Jackie Stewart courtesy of Capital Pictures:
- Justitia et fortitudo invincibilia sunt
- An t'arm breac dearg
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