导购口语:

The shirt is one size smaller than that one.
这件衬衫比那件小一号。
Does this dress come in any other color or size? I think I need extra large size.
这件衣服有没有别的颜色和尺寸？我想我需要加大号的。
I'm afraid it's a little bit big. Have you got any smaller size?
我觉得有点大，有小一点的吗？

语句解析:

Extra large size 加大号的；come in any other color or size 有别的颜色或尺寸，这里的come in不是进来的意思，而是表示“存在上市”之意；a little bit big有点大，a little bit固定词组，意思是“有点，有几分”。

情景再现:

This seems to be a bit too narrow.
这个似乎太窄了一点儿。
It's a little large. It doesn't fit me.
大了点，穿着不太合身。
This one is slightly longer / shorter.
这个稍长/短了一点儿。