Hey there!
Genevieve from Shopify here :)
Sounds like a great idea - I've had look through the app store and I think the best options for implementing this would be a manually-selectable related products app, like Cross-Sell or Product Accesssories:
- Cross-Sell: https://apps.shopify.com/cross-sell
- Product Accessories: https://apps.shopify.com/product-accessories
There are lots of related products apps that recommend products to your customer automatically based on their popularity or the customer's behaviour, but for constructing a given outfit you'll want to select the related products manually :)
Hope that helps!
Genevieve S.