Susie Mensah tried on a lilac crochet dress in a corner of a shop called Berriez, then posed as her friends and the shop owner met her with oohs of approval, the way friends do when an outfit looks really, truly good.

The dress joined a long line of garments she and her friends tried on during a recent afternoon shopping spree in Brooklyn. They changed in and out of clothes, in search of cute outfits for the summer. Music played and gossip flowed as the “yes” piles grew.

It was like a game of dress-up at a slumber party, or a fitting-room montage from a movie. But instead of a mall or department store, the setting was a personal shopping appointment at Berriez, an Instagram store turned physical hub selling vintage and independent designer pieces with a focus on plus-size shoppers.

“When I walked in, because it’s my first time, I was like, ‘I could cry,’” said Ms. Mensah, a model in town from Toronto. “I’m like a size 4X. It’s really rare that I get to find articles of clothing that express who I am and also give me the space to explore and have fun with who I am.”

Berriez began in late 2018, when the founder, Emma Zack, 31, noticed the dearth of online shopping options for plus-size vintage. At the time, Ms. Zack would shop on Instagram for vintage clothes, buying “oversized” garments often shown on thin models, she said, estimating that they would fit her size 14 figure. But they never seemed to work, and she grew frustrated, and inspired.

“This kept happening over and over again,” she recalled. “And I’m like, ‘I can’t be the only one who’s my size, wanting to shop vintage from an aesthetically pleasing, curated Instagram store.’”

She started selling clothes on Instagram, running the business out of her basement while working a full-time job at a criminal justice nonprofit. She staged pop-up shops in New York and other cities, drawing a cult following of plus-size influencers and shoppers devoted to her collection, which she christened with the tagline “curated for curves.”

In 2020, Ms. Zack left her nonprofit job to go full time as the chief executive of Berriez. The next year, she got a studio space in an industrial building in Bedford-Stuyvesant, where she now hosts personal shopping appointments, like the one for Ms. Mensah and her friends, Lucy Knell and Roseline Lawrence, who are also models. This past fall, Ms. Zack put on the store’s first runway show during New York Fashion Week.

The shopping appointments have been in high demand, Ms. Zack said, with sessions booked almost every day in April, when she officially started offering the service. In addition to sourcing vintage pieces from thrift stores and estate sales across the country, which she generally sells for less than $100, Ms. Zack collaborates with emerging designers on extending their size offerings and creating special collections, which often cost under $400.

Some of her collaborators include Tamara Malas, Shop Journal, FiOT and Feeling Space, designers and artists who produce smaller runs, including some handmade pieces.

“As a fat person, I think there’s a lot of pressure to be subdued and kind of blend into the background and look really put together, but not draw too much attention to yourself or to your body,” said Libby Torres, a journalist in Brooklyn who has had a personal shopping appointment at the shop.

“Like, we’re big, we’re taking up space. But then I think that’s exactly what Berriez clothing and Emma’s personal style, too, has encouraged me to do,” she added.

Compared with other shopping experiences, where there is often an element of “having to explain your body” to salespeople, Ms. Torres said, Berriez was “radical” because it was comfortable and offered so many options in her size. She could shop not just for looks that would fit, but also for clothes that excited her and fit her personal style.

Ms. Zack convinced one customer, Ramona Sadiq, to get a metallic chain bra. “I’m not one to own a harness chain bra,” said Ms. Sadiq, who owns a millwork business in Queens and is now a friend of Ms. Zack’s. “That is not necessarily my thing, but I did it, and I loved it.”

Many Berriez fans said Ms. Zack seems to treat each person as if they were her sole client, working toward a goal of making them feel and look good, rather than trying to sell them everything in sight. She knows many people’s measurements, and remembers their style tastes and desires.

The Berriez studio, which shares a hall with a fashion brand and a custom lampshade company, is full of a rainbow assortment of clothing, art and accessories. The racks contain garter T-shirts, patchwork pieces, squiggly neon Popsicle-colored crochet dresses, shirts with simulated nipple rings, and patterned button-downs from the 1980s and ’90s.

On the walls, Ms. Zack displays favorite finds, like a Michael Simon sweater with a doodle of a balloon-confetti roller-coaster ride, a Heinz ketchup sweater and a giant pink wristwatch clock.

Of course, Berriez is still a business, and Ms. Zack faces her share of challenges. She now balances the shop with work as a freelance wardrobe stylist. And at times, she said, it can be difficult to sell clothes to people who have been told that their bodies should be a perpetual work in progress. But finding and selling great vintage for all bodies is a process, and one that she is passionate about. “Knock on wood, I’ve never had someone come by and leave empty-handed,” she said. “So I think that’s pretty telling.”

Ms. Mensah, the model who tried on the crochet dress, reflected on the Berriez shopping experience as she was checking out. (She ended up buying a tank top instead, but said in a follow-up call a few days later that she was still thinking about the dress.)

“I can actually go out and have zero worries and know I’m going to find something that makes me feel good, that’s going to fit, with other people who have similar experiences to me,” Ms. Mensah said. “It’s just another avenue of community-building and intimacy that I haven’t experienced.”