I’ve a character that I need to add clothes to it, but the thing is that the character’s weight is changeable, and it might be fat or skinny, and I need the cloth item to respond to these changes according to character weight without overlapping between the cloth item mesh and the character mesh, the weight is changed by a blend shape (Morph). Is there any way that I can achieve this?
In theory yes 
If you need to stick to Unity Cloth, probably easiest would be to have same weight blendshapes on the cloth, and don’t allow surface penetration.