Thank you! Looking into this now 
Product bundle - Let customers choose only one size and color for a set # of product, sync inventory
Topic summary
A Shopify merchant needs to sell a 3-pack underwear bundle where customers select one size and color combination (all three items identical), with inventory automatically syncing to individual product SKUs when bundles are purchased. The challenge is that most bundle apps allow variant mixing or don’t properly track inventory across both individual and bundled sales.
Solutions proposed:
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Custom coding approach: Create a separate bundle product with a custom template that locks quantity to 3 and disables changes. Requires additional Shopify Flow automation to manage inventory updates.
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App recommendations (multiple suggested):
- Material Manager: Links variants to “raw materials” representing each size/color combo, automatically adjusting inventory across all linked products
- Easify Inventory Sync: Creates bundle groups connecting each bundle variant to its individual product counterpart with 3:1 quantity ratios
- Profit Bundles & Mystery Boxes, BiDeal Bundle Volume Discounts, and iCart Cart Drawer: Also mentioned as potential solutions
Resolution: The original poster confirmed success after significant setup work due to many variants, though they didn’t specify which solution they ultimately implemented. Another user asked for clarification on the final approach chosen.