As you said, it’s simple and minimalistic ?? In keeping with that concept, I’ve used as few templates as possible. The fallback when no single-post.php file is present is to use a single.php file, if that does not exist, it will fallback to using index.php, which is how my theme works.
So by editing the index.php file, you will be editing the single posts template too. If you want to target only the single posts, then simply copy the index.php and rename it single.php. Then anything you change in there will affect only the single posts pages. You can use this same approach for most types of templates that you may require.
Another approach is to use <?php if ( is_single() ) {} ?> conditional tags, but that does require some more knowledge of PHP coding in order to implement it.
