link the quantity field for 2 characteristics?

Hi, Let me know if this is a stupid question, I have everything just as I want it but one tweak would make my inventory handling much easier.

I sell mattresses, I have 2 variants on each mattress, variant 1 "size" and variant 2 "with or without base"

When somebody purchases variant 2 "without a base" I would like it to change the quantity of variant 1 "size" and vice versa, So I guess two characteristics would share 1 quantity field.





I tried to achieve the end result with options but it doesn't change dynamically so It's not possible..

I can understand if this isn't something that is possible but if there is a simple tweak I'd love to implement it, thanks for your time and wonderful product:)