I’ve limited the stories on my website to 20,000 to keep to the theme of short stories.

Here are some of the classic sci fi novellas/novels over at standardebooks

https://standardebooks.org/ebooks/robert-louis-stevenson/the-strange-case-of-dr-jekyll-and-mr-hyde https://standardebooks.org/ebooks/mary-shelley/frankenstein https://standardebooks.org/ebooks/h-p-lovecraft/the-case-of-charles-dexter-ward https://standardebooks.org/ebooks/h-g-wells/the-time-machine