Hi,
What I would recommend is to have the accessories as "related products" of your coffe machine product.
Then, they would already automatically display as related products on the product page.
Then, I would create a new "HikaShop content module" via the Joomla modules manager, configured similarily to the "related products" module, with the only difference being the "relation" setting set to "products in the same category" instead of "related products".
Then, I would enable that new module in the "modules under the product page" setting of the HikaShop configuration.
Since other coffee machines would already be in the same category, they would be automatically listed by that new module.