Unity 2D, animations, character customization

Hello, I'm working with 2D animations, and this animations will require changing some part of the character for IAP. For example, if we have a warrior, we will change the armor, the helmet, the weapon etc. I want to know, what program can the artist use, to do Unity like animations , so we can import them in unity, and just change the sprites of the animations. I don't want frame by frame, because is a pain in the ass to deal with this, and there size is much higher as well.

If you can point me to tutorials, references, videos, and programs either for us (programmers) or the artists to use, that would be awesome.

Thank you guys!