Here you can find clothing, accessories and make-up for The Sims 3. These are new textures and occasionally include different meshes, which you can use the Create-A-Style tool in game, to recolour and repattern to your hearts content.
There are no separate mesh files to install, they are included as part of the texture where the items have an adjusted mesh.
This does mean that creators will need to extract the mesh in order to re-use it for new textures. At this time we are not providing technical help, Workshop files or anything else to assist with this for the simple reason that no one has any time to deal with this issue. Many items also have Workshop files which are only compatible with the 0.64 version of the Workshop and cannot be used with any of the release candidate versions.
Hopefully this will be addressed in the future, but for now the best option is to simply make the meshes yourself since they are all simple adjustments of the base game meshes.