Remember when mom said you need a pair of good work "slacks"? Well, you don't necessarily need that pleated, wide-leg pair she picked out, but she wasn't wrong. You do need a pair of slim, skinny black trousers (£67) as an alternative to jeans. You can wear them with your blazer as an alternative to a suit, add them to a silky blouse for cocktails, or dress them with a button-down for something pulled together. They're a piece you'll rely on season after season, year after year, so make sure you pick a pair that really fits you.