What is cocktail attire at a wedding for a guy?

I'm attending a wedding very soon (running out of time) and the guidance is "cocktail attire". I'm a guy and I'm not really sure what this is. A suit feels too formal, and anything less feels too informal. I don't want to look like I'm going to work but equally don't want to look like I didn't put any effort in.

Can someone help me by describing what would be a suitable outfit for a guy to wear as cocktail attire please? Thinking type of jacket, colour, whether needs a shirt underneath (matching colour?), need a tie? Can wear chinos or has to be suit trousers? What about shoes?

Finding it quite hard to find inspiration online at a reasonable price, with outfits that look suitable / match. If you're in the UK, be super helpful if you can recommend a store or website that is good for this!

Thanks so much!