@jespah,
I don't think he can go a different word without changing the emotion and/or meaning of the sentence.
When I find a cool shirt in a store I will, in my happiness, say "Hey! that's exactly what I am looking for!". That sentence is perfect. It expresses the meaning and the emotion perfectly. There is not any better way to express that. Any other wording of this phrase changes it.
If I say "Hey! that's exactly what I am seeking" or "Hey! that's exactly for what I am looking", it isn't going to express the same idea or feeling.
The reason sentences in the form of "That's exactly what I looking for." are so common in everyday English is that they are very useful.