How to create sims 4 Full body skins

Hello! i'm sure people ask this question all the time, but I could not find any threads answering this question or sharing any tutorials. So I want to create sims 4 skins, and I've already mastered what most tutorials show how to do, which is taking a premade skin made by another cc creator and creating your own face overlay or face skin on top of that skin in a editing software. I provided some pictures below of my favorite skin I created so far. Now I would like to move forward with creating my own full body skins and not using skins made by other creators, but I cannot find any tutorials anywhere. Maybe because of the NSFW nature of showing a naked body while creating a skin which is completely understandable. When I've asked on reddit others always tell me it's just like doing a face but no it is not, the sims 2D skin template has the body parts obviously in different sections which confuses me on how I would take a picture of a body like with taking a face... Seems like there is something more to it than that. I'd really love to make realistic full body skins for people's sims. Are people using pictures of real bodies to achieve this? I am so confused. 

Link to photos of my skin