Well, Heraclitus wrote in the Ionic dialect, so the closest widely read prose author would be Herodotus. However, I know of no beginning books that start you out with that.
So, I'd think any of the standard courses, starting either with Homeric (Ionic with extra bits) or Attic (Athenian, but very closely related to Ionic) would do about as well. If you plan to read philosophy further, then stick with Attic.
As for which book is simplest to use, that seems to be a matter of personal preference most of the time. If you liked Wheelock, you could take a look at the White PDF available here. It'll be somewhat different, but closer than the other primers currently available. If you want hardcopy, Crosby and Schaeffer has recently become available again, in softcover. Hanson and Quinn is also generally available in bookstores, but is an intensive course.
I personally always like to suggest people start with Homeric with the Pharr textbook, but that can be pretty intensive, too.