The category pages that rank in this niche are attribute pages. Weight collections running from lace to jumbo, fiber collections for merino, alpaca, cotton and linen, and use case collections such as sock yarn or superwash for baby items. Each needs its own copy explaining what that weight or fiber is good for, what gauge to expect from it and how it behaves after washing, because that is the information a shopper is genuinely looking for when they type the term.
Patterns are the content engine. A shop that publishes free and paid patterns gains pages that rank for the project name, link directly into the yarn they consume and get shared inside the community. Project math content ranks alongside them: how much yarn a sweater takes, how to substitute a discontinued yarn, how to read a gauge swatch. These pages reach makers at the exact moment they are deciding what to buy, and they age well because the arithmetic does not change.
Colorways are the technical trap. A yarn in forty colorways should be one product with color variants under one canonical page, while the collection of colorways deserves an indexable page of its own. Discontinued yarns and retired colorways keep their addresses with a substitution recommendation, since knitters search for them long after they leave the catalog. Filters for weight, fiber, needle size and color need clean rules so useful combinations are indexable and the rest never reach the index.