I wouldn't worry too much about the parameters with a Betta unless it was wild caught. Almost all of the Bettas you will find at local fish stores or chain stores are farm raised or captive bred at least, so they are pretty hardy. Much more important to just keep the parameters consistent and have patience make sure the tank is fully cycled before you add the Betta.
My wife has a platinum half moon in a fluval 15 alone (living his best life) and her pH is over 8 and hardness is pretty high and he's perfectly healthy and happy. Just keep it stable and keep up on water changes and you'll be fine.