the post thumbnail, scale

This should work:

You could use:

add_image_size( 'category-thumb', 220, 9999 ); //220 pixels wide (and unlimited height)

and then to display:

if ( has_post_thumbnail() ) { the_post_thumbnail( 'category-thumb' ); }

This will create a thumbnail size of 220 by “unlimited”… Set the featured image on the post, then use the display code in your theme to show the 220x??? scaled image.