Once upon a time you could create an HTML file and rename it as a TXT file. The Kindles of old could then read the file and display it as an HTML formatted file. I just tried this with my Kindle Touch and it cannot read the TXT file and does not even see the HTML file. Things change--thanks Amazon.

You can definitely use @miguelos method. There will be a learning curve to embed fonts, but it is doable and you should pick it up fairly quick. If you don't want to use calibre you can use Kindle Previewer to convert the ePub (or HTML) to mobi/KF8. It is better to convert an ePub rather than an HTML file, but you might need to tweak the NCX file a bit.