Use two wax rings and be done with it.
Unless you cut out the flange and replace it, you could be buying yourself trouble by trying to "raise" the flange with "extenders".
Extenders need to be sealed completley, or your wood floors will take the hit if there is any leakage.
Consider this; there was no leaking with the previous installation. What you had before was an older toilet bowl made before the latest improvements.