A third book?

So, several people have read Almost True and asked me a difficult question.
Will there be a third book about Ty?
I have a few answers, which all add up to one thing: I really don’t know.
When I finished writing Almost True I felt emotionally drained. So many things had happened to Ty, and I felt as though I’d been there at his side. I needed a break! I was also worried about being labelled as a writer who wrote dark, grim and serious books about dark, grim and serious subjects (although I happen to think that neither Joe nor True are particularly grim or miserable) And so the next idea I came up with was supposedly lighter and more upbeat - although it’s amazing how much angst, sex and death one can work into a story about winning loads of money. (Of course, Lia is just a draft at the moment and may lighten-up considerably once my editors have seen it)
To write a third book about Ty my agent and publishers have to be sure that it’s commercially viable - that there are enough readers out there who’ve enjoyed When I Was Joe and Almost True and would want to buy another copy.
And then I need to think up a plot that will take the story on in a satisfying way. I have a few ideas kicking around, but I need to think about whether they’d be enough for a whole book. I wouldn’t want to fizzle out after a few chapters.
In a funny sort of way I feel bad about making Ty suffer any more. Most of my plot ideas are quite tough on him, and after two books I’m rather fond of the boy. Maybe I should just leave him alone.
One of the hard things about writing my next book, Lia’s Guide to Winning the Lottery, has been leaving Ty’s voice behind and moving on. So I have to make sure that a third Ty book wouldn’t feel like a step backwards. One possibility,I suppose, would be to continue Ty's story with another narrator and a different focus-Archie, say or even Claire.
I never planned to write a sequel in the first place. When I started writing When I Was Joe I recklessly killed off Ty's dad in the second chapter (a motorcycle accident when Ty was two) My friend Anna suggested that I should resurrect him, in case I ever fancied writing a sequel. How I scoffed. But I brought him back to life - albeit totally absent from Ty's life - and once I'd finished the first book and was querying agents, I got a bit bored. I had nothing to write. Then the first line of Almost True occurred to me..and the last line of chapter four (I think it's four. When someone's sitting on Ty's bed). And I could see how to get from one sentence to the other and I was off. And when I'd found and agent and a publisher, the fifteen chapters I had written of Almost True was enough to secure a two-book deal,for which I am ever grateful.
Funnily enough I think I have a first sentence for book three. Now, just the rest to think up.
So, that’s why I say I don’t know. I’ll talk to my agent and my publishers, and we’ll see. In the meantime, if you’ve read Almost True,I’d love to know what you think. Are you satisfied with two books, or dying for more? Please leave a comment below - spoilers are fine, we’ll assume that everyone reading the comments has read both books.