How to close holes:
- Switch to Edit mode ( TAB ), switch to Edge select ( 1 ), select the border edge loop ( 2 ) by Alt-RMB-clicking on it;
- Press E to extrude, S to scale, scale it down ( 3 );
- Press Alt M and choose Collapse ( 4 );
- Switch to Vertex select, select the vertex in the middle of created geometry, optionally move it up a bit, press Shift NumPad7 to align the view parallel to it;
- Select - Select More/Less - More ( 5 );
- Shading / UVs - UV Mapping - Unwrap - Project from view* ( 6 );
- In UV editor scale it down ( S ) and put somewhere in the extra area;
- Select the same border edge again and mark it as Sharp* ( 7 ).
* - The Sims 4 Studio automatically splits imported mesh along UV island borders to prevent dark shadows from forming along sharp edge loops. By closing holes, you create sharp edge loops. By unwrapping created geometry, you make sure it will not only properly display textures, but also its UV island border will be split by S4S. By marking the border edge as sharp, you make sure the dark shadow along it will disappear in Blender, too, and the baking result will not be affected by it.
How to add thickness:
- disable Limit selection to visible ( 1 ), select the region you want to thicken ( 2 );
- Mesh - Faces - Solidify ( 3 ). Set it to 0,002-5 ( 4 );
- Select - Select More/Less - More. Press Shift H to isolate the selection. Ctrl-Alt-RMB-click on the edge loop at the bottom and delete with Delete - Faces. You can also snap it to the body by enabling Snapping ( 5 ). Unhide everything with Alt H.
- remove doubles and unwrap new geometry
