Need a good iOS text editing app fast

Hi. My Apex, which I do 99 percent of my typing on is going away Monday to get fixed and I will not have it for weeks. My computer skills are not that good and even if they were, I am not at my house, so I don't have my computer. I have a braille pen which I am going to use with my iPhone for typing. Is there such thing as an accessible text editing app that can handle plain text files: .txt, has dropbox support and can read from and wright to any folder, not just its own folder and has a different and better spell checker then the one in iOS? I don't like the built in spell checker in iOS. Also, if possible, I want this app to have a better way to select text then the normal way of doing it in iOS, because I could never get that to work. Is there such an app, and if there is, what is it? Thank you.