Width (B / D / EE / EEEE) + arch type, how do you extend Magento configurable products?

Three independent configurable axes on top of size + color: width (B narrow · D standard · EE wide · EEEE extra-wide), arch type (low · neutral · high), and optional last shape (rounded · pointed · square) for dress shoes.

Architecture:

• Width is a configurable attribute on the parent product. Each width × size combination is a separate simple product (SKU). At 8 sizes × 4 widths × 4 colors that’s 128 SKUs per style, which is why footwear catalogs hit 20,000+ SKUs fast.
• Arch type is typically not a separate SKU, it’s a recommendation attribute. PDP shows “Recommended for: neutral arch” based on the shoe’s structural data. Customer self-selects via a guided quiz that filters category-page results.
• Last shape matters for dress / formal. Different lasts fit different foot shapes. Treat as filter attribute on category pages, not as SKU axis.

The performance gotcha: at 128 SKUs per style + 500 styles, you have ~64,000 simple products under 500 configurables. Native Magento price/stock indexers slow noticeably above ~50k variants. Fixes: denormalised stock-status table for “in-stock by size + width” filtering, EAV attribute indexing tuned, Hyvä theme (Luma re-renders the picker on every interaction).