The thing nobody mentions about a good jacket is that you don't notice it working until the one week you wear something else instead and realise your whole day felt wrong without it. Not the fit, not the colour, just the absence of a layer that was quietly solving three problems at once. That's the test I use now before anything else.
Getting the size right matters more here than in almost anything else you own, because a jacket has to move with you, not just sit on you. Try it on over whatever you'd actually wear underneath, not a vest top in a changing room in July, and check the shoulders first. If the seam sits even a centimetre past where your shoulder actually ends, the whole thing will look borrowed. Sleeves should let you bend both arms fully without the hem riding up your back, and if you can't cross your arms in it comfortably, put it back regardless of how good it looks buttoned up and standing still. If you've got none at all to start from, go for something in a mid neutral, a stone, a navy, a soft khaki, cut with a bit of structure through the shoulder and body, rather than black or anything cropped. Black feels like the safe choice but it's actually the least flexible, it wants to be styled a certain way, and a cropped length narrows what you can wear under it before you've even got your coffee. A proper length, something that sits at the hip, will go over jumpers in October and over t shirts in May, which is the whole point of owning one in the first place.
What it pairs with in a normal week is almost everything, which sounds like a cop out but isn't, it's the reason this category exists. Jeans and a plain top underneath, obviously, but also a dress you weren't sure was warm enough alone, or wide trousers that needed something structured on top to stop the whole outfit looking like loungewear. It copes with proper spring wind and a damp fingers crossed October, less well with actual rain unless there's a reason it's been built for that, so check what it's made of before you trust it on a day with a forecast you don't like the look of. Over months it'll soften at the elbows and collar in a way that looks better, not worse, as long as you don't throw it in a hot wash the first time it gets marked. A damp cloth and some patience does more good than people think, and a proper clean once a season keeps it from looking tired before its time.
Tomorrow morning I'd put it over a plain jumper and straight leg jeans and not think about it again until lunchtime, which is exactly the job it's meant to do.