Bra-fit quiz, 32A through 46K with sister-size, how do you actually wire it on Magento?

The pattern I default to:

• Octane AI (best for lingerie DTC, $50, $500/mo) or Klaviyo Quizzes (cheaper, native to Klaviyo if you’re already there) hosts the quiz UI. Customer answers: current band measurement (under-bust in inches/cm), best-fitting current bra (band + cup), spillage check, gore-position check, strap-slipping check.
• Quiz logic outputs a recommended size plus a sister-size pair: e.g. “Primary: 34D. If it feels tight in the band, try 36C. If the cup gapes, try 32DD.” Sister-size math is band-down + cup-up or band-up + cup-down for the same cup-volume.
• Quiz output writes back to Magento customer attributes: customer_size_band, customer_size_cup, customer_size_region, customer_sister_band, customer_sister_cup. Klaviyo sync runs via Octane AI webhook → Magento REST → Klaviyo identify call.
• PDP filters auto-pre-select the customer’s size when logged in. Out-of-stock for the primary? Show the sister-size as “recommended alternative” with stock badge.
• Welcome flow in Klaviyo segments by size so the first 5 emails feature inventory-aware product recommendations.

Quiz completion rate runs 35-60% on signup overlays in the data I see. Conversion lift on customers who complete the quiz vs those who don’t: 1.6-2.4x. Sister-size adoption (when primary is out of stock) is the highest-leverage rescue lever, cuts “size out of stock” abandonment 25-40%.