How to set up product sub-selection without additional apps?

Hi all,

im currently setting up my store and trying to find the best solution for the following scenario without the use of additional apps.

Lets say im selling 2 different product types. Shoes and shoelaces which can be bought seperatly.

On the shoe product site, there is a selection for different shoelaces which are shipped out with that shoe.

Some shoelaces will have no additional cost (shipped for free when bought with a shoe) but some also will have a small extra amount when bought with the shoe.

How could this be solved?

Any help is appreciated. Thanks

@jean721 ,

Provide the store URL…