Whenever you see ので or なので, that's because. In this case you can say 服とサングラスを買いたかったので、ショッピングモールに行きました。 Fuku to sungurasu wo kaitakatta node, shopping mall ni ikimasita. You can also use ~を買うために which would be in English " in order to buy" Hope it helps :)

Both of the others are right, but if you're uncomfortable with the backwards order (Like I am) you can use だから (Therefore) ふくとサングラスを買いたかっただから、 ショッピングモールに行きました。

どうもありがとうございす❤️❤️❤️ I prescien that

I went to the mall because I want to buy some clothes and sunglasses. A: I went to the mall --->Shopping mall　ni ikimashita. ショッピングモールに行きました。 B: I want to buy some clothes and sunglasses. -->Fuku to sangurasu wo kaitakatta. ふくとサングラスを買いたかった。 B node A Fuku to sangurasu wo kaitakatta node Shopping mall　ni ikimashita. B kara A Fuku to sangurasu wo kaitakatta kara Shopping mall　ni ikimashita. A nazenara B Shopping mall　ni ikimashita nazenara Fuku to sangurasu wo kaitakatta (node/kara). （This is not common way to say, it is a bit formal way, however, if you are English speaker, it is easier to remember because the sentence order is the same. ) Good Luck with your Japanese Study :-)