My sims tend to look somewhat the same because I apparently have a one-tracked mind about how sims should look. But, they don't HAVE to look the same. You just need to play with the sliders a lot. Sometimes for me, it works to either find a premade somewhere in EA's worlds that I like to use as a base for a new look or to download another simmer's sim creation. There is a lot of CC out there, including some contouring type things that help change a sim's looks, but I've used very, very little of it so I'm not the best person to help there. Just don't download sims with CC from the exchange where you have no idea what CC was used or where it came from because you can accidentally introduce some problematic things to your game that are hard to track down. It's far better to go straight to a reputable CC creator and get it that way.