40s: By now, you know what you like. Thick, substantial fabrics. Fits that won't make you look like a kid (or a geriatric). Staples you can wear out during the weekend or to the office. For your basics, you're looking for jeans, shirts, and sweaters that have class — and since you'll be wearing yours with sky-high pumps and boss-lady jewels, make sure your fundamentals have good bones to start with.

Cashmere Sweater — The color options and feel are impeccable, and the fit is not-too-snugly and not-too-loose, just how you like it.
Equipment Crew-Neck Sweater, $407, available at Matches.

T-shirt — James Perse makes high-quality, opaque white shirts that you won't have to worry about peeking out from underneath. Plus, the longer lengths make them perfect for tucking in.
James Perse T-Shirt, $50, available at Net-a-Porter.

Jeans — For elongating, slimming jeans, Acne really can't be beat. Plus, its thick denim will provide you the support you're looking for in a pair of pants.
Acne Marine Flex Jean, $270, available at La Garconne.