Best way to get best breadcrumbs for Commerce
You can add breadcrumbs in your page using drupal_get_breadcrumb and drupal_set_breadcrumb function

In template.php

 function THEMENAME_preprocess_page(&amp;$variables, $hook) {

        if(arg(0)=='shoppage'){  //Put appropriate condition 
            $breadcrumb = drupal_get_breadcrumb();
            $breadcrumb[1] = l('Shop', 'shop_link');
            $breadcrumb[2] = l('Category', 'category_link');
            drupal_set_breadcrumb($breadcrumb);
        }
    }