Hi @BPH_Marina_Alta ,
Sorry for the late reply I just read your question, I understand your requirement. In your case, the said product has 3 variants. The first 2 variants are single SKU products i.e. left and right, while the last variant is a combination of the first two, called "Both”, which is a multi sku bundle consisting of the “left” and “right” product variants as child items.
With our app, you can achieve this easily. You would just need to create a bundle for this specific product variant i.e. Both. The customer’s experience would be as follows: when they select “Both” on your product page and click “Add to Cart”, then proceed to the checkout page, the app will separate the bundle and display the single SKU products in the checkout itself. On the backend, when the order comes in shopify order admin, it will only consist of single SKU products for ease of fulfillment for your team.
I hope this is what you’re looking for, Our team is just one email away should you need further assistance. Feel free to send us a message anytime. 
we also have option for 1:1 online meet with our experts where all of your queries would be answered in that session.