Two HC-05 modules won't stay paired

No, there is a 5V to 3.3V regulator on the module. The Martyn Currey tutorials linked above really are the best.

Do you realize that this loop floods the "air waves" with a nearly continuous stream of 1s and 0s? That flood of data might cause the disconnection.

   // Reading the button
    buttonState = digitalRead(button);
        if (buttonState == HIGH) 
        {
        Serial.write('1'); // Sends '1' to the master to turn on LED
        }
        else 
        {
        Serial.write('0');
        } 
     delay(10);

It would make much more sense to send the switch state at longer intervals, or better, when the switch state changes.