I may have a tip for you, you should make an animation, for like 30 frames, where the first frame is the T pose, and the last is the end post of you char, and make your bench / chair or the thing that your character sits on starts a bit behind at frame 0 and get to the position for frame 30
Then you simulate with the animations, it gives much better results and no clipping (except if you change it yourself after)
Here's a little result of how it looks after
View attachment 718220
Quick edit to add that it's probably better if you make it like 15 frames, and the last 15 frames for the dress to stabilize and all, I don't simulate much since I rarely use dresses that needs it, but the best to do is to experiment around that.
Note that it may take a bit longer to simulate that way too. But it's not that much longer so