I was searching for an iOS text editor / word processor that could use fixed-width fonts, and Notesy seemed to be the only one. It's a bit expensive. Strangely, it doesn't support formatting or colours in notes. It seems to be just a plain text editor. Maybe it leaves formatting to Markdown.
Notesy supports "Markdown", which is like a very simplified, unobstrusive type of html. It lets you do basic formatting like headers and lists.
One problem was when viewing in MD mode (in which iOS renders it as html), my numbers kept being converted into links, which was irritating and messy. iOS automatically converts numbers into links in notes, emails and webpages. To prevent this, you can add this code:
Surprisingly, this works in Notesy too! Go to Settings > Markdown and add it into the Markdown Header box.