saving values with PlayerPrefsX

Hey i want to start using PlayerPrefs to save things in my game. I imagine if i know about saving one thing i would know on how to do for the rest of them. Using PlayerPrefsX and i want to save a bool.

The bool is called "isSaved" and the name explains itself. The bool is at default false and it will check if i save the game and with this bool being true i can "continue" the game and the bool will be set to false once i create a new game (the saved game will be lost, the game is reset etc.)

The "New Game" and "Continue" functions are set in buttons in the game aswell as the Save button. I want the bool to keep its save through scene changes and also when i enter and exit playmode.

How should i define this bool first? using public or private? static? And how can i make sure the bool wont be changed unless i manually tell it to.

Thanks