Just noticed that when I use Startup Pro as my main theme, I get the alternative of choosing templates with posts– apparently the same templates as those offered with pages. But I was using a child version of Startup Pro and don’t have that ability with posts.
Can I not get post templates with a child version of a theme?
Custom post templates are an exclusive creation of StartupWP, we’re not aware of any other theme in the world that supports custom post templates. With that in mind, this is a very special feature and not widely supported. Not sure why exactly a child theme would throw a wrench in the works, but the easiest way to create a new post template is to just copy one of the others (template-sidebar-none-post.php is probably the closest to the default post template), change the filename and change the bit at the top: