"自分が持ってる服に合うかどうか"
- Does it go with the clothes that I already have.
- Does it match the clothes that I have.
- Does it fit the clothes that I have.
服を買う時、今自分が持ってる服にその服が合うかどうか考える。
When buying clothes, I think about if the clothes mix and match that of I’ve already.
最初の方は大丈夫ですが、"mix and match that of I've already" は少し不自然です。
言いたかったのは "match the clothes the clothes that I already have" だと思います。
- When buying clothes, I think about if the clothes match the clothes that I already have.
- When buying clothes, I think about if they go with the clothes I have now.
When buying clothes, I think about whether they go well with what I already have.
「自分が持ってる服に合うかどうか」は、「I think about whether they go well with what I already have.」で表現できます。
Go well with は「合う」や「似合う」という意味で、自分の持ち物や他のアイテムと調和することを示します。
What I already have は「すでに持っているもの」という意味になります。
アメリカ合衆国 
