Will fish oil help with hairballs?

I've been giving petromalt to my one cat that was vomiting several days a
week. Along with more brushing, the problem has subsided considerably.
I'd like to give them an oil they would like, and I think they would like
fish oil. Is it safe to give them fish oil several times a week in their
wet food? Also, would olive oil have the same benefit of lubricating
their insides and helping them pass hairballs? I've read that mineral oil
(like in the petromalt) works, but there can be issues with the cat
inhaling the fumes. I've also read that cod liver oil is too high in
vitamin A.

-Thanks