I feel like the answer to this is going to be immediately "yes" but hear me out

My boyfriend doesn't own a suit, and hasn't since he was little. As a designer, he works in mainly creative environments and pretty much wears what he likes to work- usually boots, slim dark jeans, and a collared shirt with a sweater/cardigan on top. He even gets away with a version of this look for interviews (obviously with very new, pressed items). He loves clothes and dressing well, but so far has never needed to invest in a suit.

The reason this is coming up now is our friends' wedding in Canada next month. He assumed for a long time that he'd have to buy a suit for this, and I did as well. The other day we were talking to my sister, though, and she reckons that he can get away with something slightly less formal, either his regular look with a jacket on top, or a shirt/tie/cardigan combo with dressier wool trousers. I haven't been to a wedding for a good ten years now, so I don't know either way.

If he decides to get a suit, it's going to be tough. He's very picky about fit (which is good!) but finds it difficult to find clothes that fit well. He's a slim guy with broad shoulders, so I think the jacket would be the hardest thing to find. He doesn't mind spending money on good quality things, but I'm less inclined to encourage him to get something super-expensive if he's going to wear it so rarely.

So, what do you think? What would you suggest for a clothes-loving but hard-to-fit guy who likes the idea of formal clothing but doesn't have the lifestyle for it?