Dawn shopify product variants incorrectly affecting inventory available

[hnaegele]

Hoping someone can help me out here - I'm having issues figuring out how to reflect accurate product inventory counts when I start adding variants into the mix.  On my page - https://29and11.com/products/3-5-6-pendant. you can see that the pendant is offered with three variants - size (A small or large), a chain type (3 different chain styles) and chain length (16, 18, and 20).  The chain length doesn't affect price so I was able to use the Shopify UI Elements Generator to add a field for the customer to select the chain length.

But the price of the pendants varies with the chain style, so I can't do the same with that.  Shopify will let me add the price to the chain style variant, but it also requires me to assign a quantity.  The issue is - I don't want to assign a quantity to the chains because my stock of those is large enough that I'll always have more than the pendants.  For example, if I only have 20 of the small pendant, how do I get the quantity available to reflect change only when a size is purchased?  I've attached a picture that I hope will help understand my predicament.

Thank you!!