Configurable custom field selection in the product

-- HikaShop version -- : 5.1.5

We are creating a webshop with clothing. I've added custom field of type item with the sizes: S, M, L, XL, XXL
The field is now added to every product, but for certain products certain sises do not apply. Is there an option to select on a product basis what sizes apply so the visitor can select the prices? Now we have different custom fields with different ranges. For every product we now have to go into the custom field and selects the products to make sure the size range is applied, which is a lot of work.

Is there a way to select the sizes in the product backend that can be selected in the frontend?
Note: all prices are the same so setting up product characteristics is a bit of overkill.

Thanks in advance.

Could this be a solution?

create a product custom field with sizes checkboxes so in the product backend the sizes can be selected.
Next create an item custom field with options that is filled using an SQL query using the current product ID? The thing I don't know if the current product ID is accessible via the MySQL query field. If os could you give me an example?