Base product vs variants

I sell prosthetics on my Squarespace website, and offer the option for add-ons like paint, hair, etc. I have those listed as variants currently at different price points, but they all come out of the same stock. The problem is that Squarespace doesn't seem to be built like that, so I have to do the actual stock number for the basic prosthetics and set each variant at unlimited and hope somebody doesn't order more of those than I have in stock. Very annoying.

Is there a way to make Squarespace understand that I'm selling 10 of something. Want it painted? Still comes out of that 10. Painted with hair? Different price, but still comes out of that stock of 10.