What is breast fat grafting surgery?

I'm curious because of my partner who has a chest complex.

I have a reluctance towards implant surgery, so I do not like breast plastic surgery.

But I became curious because I heard fat grafting is also possible. That surgery seems much more natural and has fewer side effects. Is that really true?

So, the cost would be much higher, is that really the case?

Please let me know how it is. If the cost is reasonable, I think it might be worth trying.