Answer:
ANSWER
Please bear in mind that Italian is a language and not a dialect.
In Italy there are a lot of dialects. Each region has his own dialect and even each town or city pertaining to the same region could have a different one.
Anyway "the one I want" could be translated into Italian as "quello che voglio", in the sense you want a specific object; example: "There are three watches on the desk and the one I want is that in the middle".
"You are the one I want? Italy has 20 dialects, and they are considered not elegant. I would say:
Sei ciò che desidero