Women's Knitwear
Knitwear is built to stretch to the body in a way woven fabric isn't, so a sweater's flat, laid-out measurement is deliberately smaller than how it will actually sit worn — a size medium knit can measure closer to a woven small before you put it on. That's the fabric doing its job, not a sizing error, but it also means a flat measurement alone can't tell you how a sweater will fit the way it can for a shirt.
Fibre content decides how well that stretch survives repeat wear. Wool and wool blends have natural elastic recovery — they stretch to fit and spring back. A pure cotton knit stretches too, but recovers poorly, so a cotton sweater tends to grow and stay grown at the elbows and hem over a season, while the same cut in wool or a wool-elastane blend holds its shape longer.
Gauge (how fine or chunky the knit is) is the other variable a size label doesn't carry: a fine-gauge knit sits closer to the body at a given size than a chunky-gauge knit in the same nominal size, because the chunky yarn itself is adding bulk the pattern has to account for. Checking the fibre composition line next to the size chart tells you more than the size number alone.
Women's Knitwear at retailers

COS
Layered Merino Wool Sweater

COS
Merino Wool Sweater

COS
Animal Jacquard Merino Wool Sweater

COS
Belt-Detail Merino Wool Sweater

COS
Balloon-Sleeve Merino Wool Sweater

COS
Sculpted-Shoulder Merino Wool Sweater

COS
Rounded Double-Faced Wool Sweater
Aritzia
ATTICUS MERINO WOOL SWEATER
Aritzia
BYLINE MERINO WOOL SWEATER
Aritzia
OATS MERINO WOOL SWEATER
Aritzia
ATTICUS MERINO WOOL SWEATER
Aritzia
BYLINE MERINO WOOL SWEATER

Banana Republic Factory
Merino Wool Ribbed Sweater

Banana Republic Factory
Merino Wool Johnny-Collar Sweater

Banana Republic Factory
Merino Wool Turtle-Neck Sweater

Banana Republic Factory
Merino Wool Boat-Neck Sweater

COS
Merino Wool Funnel-Neck Sweater
Calvin Klein
Calvin Klein Women's Merino Wool Polo Sweater - Ivory - XL
Calvin Klein
Calvin Klein Women's Merino Wool Polo Sweater - Red - XL
Calvin Klein
Calvin Klein Women's Merino Wool V-Neck Sweater - Dark Pink - XS