You can easily handle books that come from outside the Amazon store on your Kindle Touch. First, if the book is DRM free, you can either "sideload" (copy) it to the Kindle if it's MOBI formatted, or convert it using Calibre if it's ePub formatted, and then sideload.
If the book is DRM'd, you need to strip the DRM before you do much of anything with it. This is NOT HARD, but we can't give you any more specific instructions here than to tell you to "google Apprentice Alf".
Even if you never buy a book outside your eReader's native ecosystem (Amazon, for me), removing the DRM is just smart since it allows full and flexible backups. My normal workflow strips the DRM on every book I read before I start. It takes a few seconds longer, but since Calibre would be part of my eBook management regardless, it really isn't an issue.
If you like the Kindle Touch, get it. Then address the minor annoyance of how to make sure you have flexibility with any books you buy. And maybe someday the publishers will get rid of this crud, just as the music industry finally did.