Variants are the architecture decision
Most apparel projects that go wrong do so because the variant model was decided casually. Colour as a separate product or a variant option, size runs that differ by colourway, fits that are really separate products — each choice determines what merchandising, filtering and stock logic can do for years afterwards.
It is worth spending real time on before the build, because changing it later means re-cutting the catalogue and every URL attached to it.
Returns are a storefront problem
The instinct is to treat returns as logistics. In apparel they are mostly a product page problem: the customer could not tell whether it would fit, so they ordered two sizes.
That reframes the work. Measurements, model information, consistent photography conventions and clear fit notes are conversion work with a direct margin effect, and they depend on product data being structured enough to display consistently across a changing range.