I have been adding clothes to my wardrobe, but the number doesn't increase. Is there a certain page I need to go to?

This achievement is currently broken in the current wardrobe, there isn't a way to trigger it so the only thing that can be done is wait for a fix (can keep adding items so when it is fixed could get several tiers at once)

There is a bug forum topic: here, there isn't an ETA on this getting fixed though