错了,
正确的说法是：
I saw something in the paper that would interest you.
这里是不定代词做为先行词,用that引导,不用which
或者可以说 I saw something in the paper that you would be interested in.
对补充
之所以改成would interest you是因为从句的主语是that或者which,而interest在这里是做为动词,表示使感兴趣.做为从句的谓语动词.假如是you would interest 就和主句的something连接不上,要么就改成you would be interested in,.something就做in的宾语