Body clipping and armpit glitch - in game

Hi.
The clipping issue is caused by the choice of the item to start the package. You cloned a swimsuit that is made of 3 meshgroups: the lower calf area, the upper calf area, the rest of the body. The swimsuit is made this way to properly interact with tall boots. You imported a blend file that has only one meshgroup that replaced the one in the lower calf area with the corresponding cut number. More about it here
Anyway, the solution is to clone a lingerie set.
- always try to make the garment tight in the armpit area. This will ensure the weights will transfer right. If you want to make an item with loose sleeves, it will have to be done with arms down because this is how the sims stand most of the time;
- do not use md's automatic retopology tool, it only makes it worse. If you have md11, try their new retopology tool. If not, model in quads and keep the particle distance high. Your dress has no fine sculpted details that need to be preserved, there is no need for the polycount to be that high;
- on the subject of what is and is not needed. If you plan on sharing your item with other people, you should be conscious of the fact that others may want to use it with accessory like scarfs, outwear, etc. There is no official space for these items, so people often use the extra space in the bottom right corner where your sleeves are. So we always recommend people to avoid that region altogether because everybody puts everything there and you end up with CAS full of items that cannot be used together. So use the body's uvs as a reference for how to arrange yours. Also, again, the dress does not have much going on in terms of fine details, there is no need for it to have very big uv islands;
- and on the subject of uv islands, do not scale them individually ( if you did that, the sleeves are a bit smaller) if they are meant to share the same texture/pattern. You can make buttons or zippers bigger or uvs of the geometry that covers the holes smaller but everything else should be scaled together
- when closing holes, make sure to not only scale the extrusion down but also collapse it, this will reduce the polycount by half. So E to extrude, S too scale down, Alt M - collapse. Then you should unwrap the created geometry ( quoted text only );

I do but no start-to-finish ones, they are not particularly informative in that sense, more like for resolving specific problems (how to make clothing with loose sleeves, how to edit weights, how to transfer uv_1, retopology in zbrush which I no longer recommend)