Welcome to Sun Sims, Auntie Thorn!
I have a fleet of Macs, but I play The Sims 2 on a PC and have no idea what meshing utilities might be available for MacOS. Since so many movies are produced on the Mac I would guess that there are lots of them.
Maya by Autodesk is available for (actually written for) MacOS X, but it's
beastly expensive. The last I heard, the sticker price was about $5,000 so it's definitely a rich kid's toy. On the other hand, I've heard rumors that it's possible to use the Maya Personal Learning Edition (Maya PLE) to generate 3D models that will work in The Sims 2, and the PLE is free. It might be worth looking into!