You can basically use every oil for massaging. It's basically just to make it easier for your hands to slide over your boobs.
So I started with olive oil because I had that at home. Guess that's why you are asking if sunflower oil is okay, right?
I then started using cocunut oil cause I read it's good for NBE but my boyfriend hates the smell
so I stopped using it and switched to an pharmacy oil which doesn't smell at all.
But it has some benefits like reducing stretchmarks and stuff. Working out fine so far.