“Isn’t a novella just a short novel?”
In a word, no.
When you write a novella, you have a smaller canvas on which to tell your story, so you’ll have a smaller cast of characters, and fewer complications.
That said, you need as much suspense for a novella as you do for a novel; a focus on character development is vital.
Consider novellas for your self-publishing plans (they’re fast to write)
Novellas are faster to write than novels. With a word count of between 20,000 and 40,000 words, you can produce two novellas in the time it takes you to write one novel.
(If you wish, you can write a novella in seven days.)