Yes you can use Olive Oil to help firm up your breasts since the fatty acids contained in Olive Oil can help to reverse the damage of free radicals which helps to perk up and firm the breasts.
You can use the Olive Oil in tandem along with massaging your breasts.
Chest exercises can also help to firm up breasts as well as prevent the breasts from sagging.
You can also use Jojoba oil, argan oil and almond oil to help firm your breasts when massaging them.