Becca: Thanks for the clarification - just checking that this was a short document and not, say, a novel-length piece. That makes things easier!

Honestly, I would say your best bet is to code the thing by hand in Sigil - I hand-code and convert my .epub files to .mobi format all the time with Calibre and rarely run into any problems. With a bit of help from online HTML and CSS tutorials, you should be able to whip this up pretty quickly - Sigil's stylesheet file is your friend!