Set featured image to archive.php

Question

At the moment I create a new page, set a featured image and link a certain CPT template to show all those CPT's (by using a query) with the featured image on top. However, this is in my opinion the wrong way to do this because each time I create a new CPT I'll have to create a new template. My page types now look like "default, cases, products, clients, ..." which is not the purpose of a template.

I tried using archive-CPT.php which will automatically loop through the correct CPT but the problem is that I can't use a featured image anymore. I could, but I want to change/remove/add the image via Wordpress like I do with pages...

How would I be able to achieve this the right way?

EDIT: archive-clients.php

<?php
  while( have_posts() ) : the_post();
  $header = get_the_post_thumbnail_url();
    $title = get_post_meta(get_the_ID(), 'page_title', true);
    $subtitle = get_post_meta(get_the_ID(), 'page_subtitle', true);
?>
<header class="page-header about-header" style="background-image:url(<?php echo $header; ?>)">
  <h1 class="page-hero-title"><?php echo $title; ?></h1>
  <h2 class="page-hero-subtitle"><?php echo $subtitle; ?></h2>
</header>

<?php
  endwhile; 
  while( have_posts() ) 

: the_post();
?>

<div class="row clients">
  <?php while( have_posts() ) : the_post(); ?>
    <h1><php the_title(); ?></h1>
  <?php endwhile; ?>
</div>

<?php get_footer(); ?>

Answer 1

In my opinion the right way to do this is to create theme options. Create a field asking the desired image for the clients post type archive.