One of my white whale wardrobe items of the past ten years has been a pair of black velvet Alaïa leggings. I once saw the model Jamie Bochert leave the backstage exit of a fashion show during Milan Fashion Week in her own pair, worn with a thin, oversized white tee and black Chanel ballet flats . The effortlessness of this outfit, with her signature messy hair, left such an impression on me that my irrational need for these leggings has lasted nearly a decade. I never could muster up the guts to plunk down the $1,300—at the time—for a pair of leggings, even the seemingly perfect pair. No matter how many ways I tried to “girl math” them—cost per wear, push present from me to future pregnant me, freelance fashion editor tax write-off, etc.—it just never made sense to me. Since that initial sighting, Mr. Alaïa has passed away, inflation has skyrocketed, the brand has gained a new creative director, and now the same pair currently retails for $1,900.…