Is it a Novel, Novella or Novelette?

That's what I now ask myself about my current WIP. I came to a decision on how to end it, but now it seems to short to be considered a novel. The current word count is 17K-something.

At least that's what this website says. Anyone care to argue otherwise? 🙂

I know that some kids' books are quite thin, would that be acceptable in my case? But here I read this about graphic and epistolary novels for kids:

I now wonder what I can consider an appropriate length for my work, since it's an epistolary book. I don't plan to make it a graphic novel, since I'm not that great will illustrations and if I want it to be illustrated, I'll have to have to get  someone else do that part 🙂

I also wonder if I should and how I can make my WIP longer. I now have some other ideas for the protagonist, but think that these should be another story altogether. The plot has been mostly about the boy getting braces. He's on the brink of becoming a teen and that could make for another book plot line. Or could this be all one book? This is making the title even harder to find. L

Lots of decisions to be made now.