Add product variants with logic

Site URL: https://www.flabelus.com/kid/p/meg-kids

Hello everyone! Im trying to allow the customer to add some customization for their products, as it appears here:

Basically, what i need is that IF one of the options with additional price is selected that the customer can add some letters in a text field (or custom form) but if no addon ($0) is selected that doesnt appear.

You can see an example of how its done now: Example for custom add-ons with custom form

The problem is that if the customer selects: "Sin iniciales (+$0)" , the custom form still appears.

The BEST way would be having it exactly as in here

We dont mind paying for a plugin like this or a personalized solution to implement it. 

Will be great also that we dont have to add all the variants to all products and sizes (this is how it has to be done actually from squarespace.
All options will be the same for ALL products.

Any help or potential solution?

Thank you very much in advance!