The thing nobody tells you about building work outfits around a blazer is that the blazer should be slightly too big in the shoulder rather than too small, because a tight shoulder seam is the one fit problem you cannot fix by rolling the sleeves or pulling the sides in. Everything else about the outfit can flex around the day you're having. That one can't.
Colour wise, I've gone through every option and keep landing back on navy and a soft charcoal grey, because black can look like you're off to a funeral by nine in the morning and camel shows every coffee drip within an hour. Navy goes with cream, white, pale blue, even a faded black trouser without the two blacks arguing with each other. A check in muted tones is lovely too, but only once you've got a plain one doing the daily work, otherwise you end up looking like you're trying very hard on a Tuesday. I had a bright cobalt one for about a year that I loved on the hanger and wore maybe four times, because it wanted the rest of the outfit to be quiet and most mornings I can't be bothered negotiating with my clothes before eight.
For occasions, this whole way of dressing earns its stripes on the days that aren't glamorous but aren't casual either, a meeting that matters, a client lunch, a school pickup straight after work where you want to look like you've got it together even if you spent the morning arguing with a printer. Over a plain t shirt and straight leg trousers it reads as effort without trying. Thrown over a midi dress with boots it carries you from a cold morning into an afternoon where the heating's cranked up and you need to lose a layer without losing the outfit. Autumn and early spring are its best months, when you need the extra layer but a coat is too much for sitting at a desk all day.
If you're starting from nothing, buy the single breasted one in a mid grey or navy, in a fabric with a bit of structure rather than anything jersey or soft, because the soft ones look brilliant on the first wear and like a cardigan by the third. Skip the double breasted version until you already own one you trust, it's a lovely shape but it asks more of you underneath, you need the rest of the outfit to be simple or it all gets a bit much. A longline one is forgiving over most trouser shapes, a cropped one wants a higher waistband underneath it or you'll spend the day tugging things into place.
Try it on sitting down before you buy it, because that's when a blazer that looked fine standing at the mirror suddenly pulls across the back.
