Navy has this reputation as the sensible alternative to black, the thing you buy when you want colour without the commitment, and mostly that reputation is earned. It's not exciting. It doesn't need to be. I've got navy tops that have outlasted every trend they quietly ignored, and that's the whole case for them really.
If you own nothing in navy yet, start with a plain crew neck in a mid weight cotton or a cotton and modal mix, nothing sheer, nothing that needs ironing before it looks decent. That's the one you'll reach for on a day you haven't planned an outfit, which is most days. Once that's bedded in, the long sleeve version in the same fabric earns its spot too, because navy under a jacket reads smarter than grey and softer than black, and that's a useful trick to have. The shade matters more than people admit. A navy that leans slightly towards ink or midnight sits well against most skin tones and most other colours you already own, whereas the ones that drift towards a bright, almost denim blue can look a bit costumey under certain light, more sailor fancy dress than considered top. Hold it up near a window before you commit, not under shop lighting, which flattens everything into the same blue.
Before you buy, check the seams at the shoulder and the hem, because navy dye is notorious for fading unevenly, and a cheap one will go slightly grey at the stress points after a handful of washes while the rest stays dark, which looks less like a worn in favourite and more like a mistake. Check too whether the fabric has any give across the chest, since a stiff navy top with no stretch will crease exactly where you don't want it to, right across the middle, and sit oddly under a coat. A good one should come out of a bag at the bottom of your luggage looking only mildly sorry for itself, not needing a full rescue with a steamer.
Navy pairs with nearly everything in a normal wardrobe without trying, which is the actual point of it. White or cream trousers, blue jeans a shade or two different from the top itself so it doesn't look matchy, a camel coat over the top, gold jewellery rather than silver if you want it to look a bit more done. Wear it under dungarees, wear it with a grey skirt when black feels too heavy for the season, wear it on the days you genuinely cannot face making a decision about colour.