Adding an image to blog post category overview

I would like the category overview to show images to the side of the blogposts. I like the icons for the types of posts, but I would really like it if I could have the images set as featured images on the right side of the category overview. I know I would usually need to add <?php the_post_thumbnail();?> before the content loop for it to work, but I cannot find the content loop in gridmarket. Or should I grab that from framemarket? I would rather not do that as that would influence updating framemarket...

Your thoughts are appreciated!