@Asira
I do my Body-Swaps completely in Unity, though it is more optimized to do it in Blender. This is the tutorial I used, it might seem kind of daunting but it's actually super duper simple. >> TUTORIAL VIDEO
I don't know if the tutorial includes this, but my tip is to make sure that you anchor everything to the same part so that the shading is consistent. If you don't know what that means:
Click an object, and look at the display on the right and towards the bottom above where the materials are listed there will be something called "Anchor Override". Some models have a specific thing in there armature they use as the anchor, but not usually. If it doesn't have a specific anchor I would use the chest. Simply open your armature and grab and drag the "Chest" part of your armature into the box. You can also just use whatever the body part of your model is already using. I would to this for everything on your model, clothes, accessories, etc.
You'll also need to edit the textures to match the skin tone like I mentioned above. You should make sure that both the materials are using the exact same "Shading" settings so that it is as seamless as possible. You don't need to be too precise since the hair will obscure the head and neck so if the colors don't match it isn't the end of the world, but it is nice to get the colors as close as possible.
