Stepping can be done on a weekday in 9 days when not worn before.
B’dieved
As far as wearing weekday clothes on Shabbos, you are mistaken. It’s hachana.
The only heter is clothing you really could wear on Shabbos (such as a white shirt) and on Shabbos morning, instead of putting on your shirt from Friday night, you out on a fresh shirt, that’s okay. Same when waking up from a nap.
But stam trying on clothes that you don’t need to put on is hachana.