In 1985, when Donna Karan launched Seven Easy Pieces, the collection of stretch jersey bodysuits and separates intended to underpin every woman’s wardrobe whatever the season, she said, “I’m designing for an international woman. A creative person who never knows where a day is going to take them.”

Thirty years on, Karan has stepped away from her label but the trans-seasonal concept is more relevant than ever. With our increasingly globetrotting lifestyles, wardrobes are becoming less and less delineated. The notion of trans-seasonal dressing (clothes that work beyond their allotted autumn/winter or spring/summer slots) has for some time been on the minds of designers and buyers; now it is becoming the norm for shoppers.

“Seasons are becoming less relevant because the customer no longer thinks in those terms,” says Sarah Rutson, Net-a-Porter’s vice-president of global buying. They are increasingly drawn to “buy-now, wear-now fashion with longevity,” she says. “The concept of shopping ‘out of season’ is becoming obsolete because the market-space in which we operate is global.”

Our wardrobes reflect lives that are packed with travel across time zones and climates. “It’s about investing in quality product that you can wear all year round — the perfect pant, the shirt, the blazer you can layer,” says Rutson. Clothes that suggest simplicity and co-ordination — while, importantly, looking au courant.

Lesson one: don’t confuse trans-seasonal dressing with playing it safe. A host of designers have perfected clothes that elegantly negotiate crossing into a new season. LA-based Rosetta Getty is attracting fans with a version of laid-back luxury delivered in the shape of long cotton shirt-dresses, sleeveless cashmere cardigans and wide-leg cropped trousers — all ideal for layering as temperatures fall.

In New York, Tomas Maier has reinvigorated his eponymous line, making clothes suitable for any climate, while The Row is establishing elegant column skirts, softly tailored jackets and tonal tunic dresses that appeal to both jet-setters and the fashion-literate. Christophe Lemaire specialises in lightweight macs, woollen wrap skirts and cotton apron dresses while other pin-ups for this movement include Caroline de Maigret, with her wardrobe of wide trousers and artfully crumpled men’s shirts, and Marni’s Consuelo Castiglioni, who mastered layering long before the rest of the world caught on.

“Each time you buy a piece from these brands it’s like collecting something for your wardrobe that you know you will own for a long time,” says Alex Eagle, creative director of The Store Berlin and Alex Eagle Walton Street in London. As well as stocking many of these designers, Eagle recently launched her own line, which she describes as comprising “components that are multifunctional without being complicated, things that you grab when you’re getting ready in a hurry and need to look pulled-together”. The capsule includes a scarf-neck dress that doubles as a tunic, tailored trousers and a silk shirt — all in black-and-white.

Here’s what to add to your shopping list: two crisp cotton shirts, one in white, one in blue (try Christophe Lemaire, Marie Marot, Protagonist and Acne for contemporary cuts and subtle details); an unidentifiable handbag (those from The Row, Myriam Schaefer and Philipp Bree 0110 are the most discreet); a round-the-clock black dress (thank you, Catherine Quin); and fine-gauge jerseys for layering from Vince or Crippen. According to Louise Trotter, creative director of Joseph, “It is all about longevity and classicism with a bit of an edge. Clothes with slouch, a relaxed fit and quality are our best sellers.

We have started to see easy, unfussy pieces with more masculine cuts getting attention over the structured silhouettes of days gone by.”

Blazers are an excellent solution for bridging seasons but be sure to opt for an elongated, masculine cut; throw over a sleeveless summer dress or team with co-ordinating trousers when autumn knocks. The label Blazé Milano was founded by three Italian fashion editors, Corrada Rodriguez d’Acri, Sole Torlonia and Delfina Pinardi, with a simple goal: “One product, made well, and made in Italy.” Their handmade blazers come in heavy wool, silk matelassé, raffia and mid-weight linens, although Pinardi explains that the use of heavier textiles such as loden, mohair and heavy wool allows their blazers to be worn “like a little coat, in the winter or in a cold city”.

White, black, grey, navy and camel are shortcuts to a cohesive wardrobe but it’s not all about desaturating your colour palette. “I have a dress by Rosetta in bottle green which I live in, and she is now doing an exclusive for us in her beautiful red silk,” says Eagle.

Likewise, Rutson notes the impact of Chloé’s dramatic maxidresses (“a continuity piece to be styled up with sandals in the summer and boots in the fall”) and Gucci’s colourful separates (“ideal for trans-seasonal dressing by partnering statement blouses and pants with season-specific items”).

Does it all sound a little serious? Loosening the reins on your accessories will enliven an otherwise pared-down look. Trotter relies on great shoes to lift her wardrobe go-tos, while Eagle recommends Alice Cicolini’s enamel gobstopper rings to prevent an outfit from becoming subdued. Also worth noting is Sophie Bille Brahe’s contemporary range of pearls: understated and luxurious. As Caroline de Maigret said: it takes effort to look effortless.