What is the idiomatic way to say "clothing fits"?
I am a native Chinese speaker and glad to help you.
In Chinese, there is a more idiomatic way to express that the clothes do not fit.
You can simply say "合身".
As an example: 这件衣服不合身, 它太大(或小)了.
(Translation: These clothes do not fit me because they are too large (or small).

When you use "适合", a misunderstanding may occur. This word can also be used to describe how the clothes look on you. (Just as your example: you use it to say you don't like the style.
As an example: 这件衣服不适合我, 它显得太年轻了.
This means these clothes are often preferred by younger people.

When you say: 这件衣服穿不上
You only emphasize that these clothes are too small for you.