Here is your link to Scarier Horror Play. This is the follow on book from Easier Solo Play. It is not explicitly Solo, but much of it does apply. What is good for general RPGs is also normally good for solo.
Many of the examples in the book come from my own solo games.
Here is your link!
https://www.drivethrurpg.com/browse.php?discount=909692b434
This has also been added to the back catalog post.