"I look forward to working with you." seems more concise.
There doesn't seem to be any problem that I can see of your ending the sentence with "you". I can only suggest some rewording:
"I look forward to the opportunity of working with you."
If you want to be more creative you could expand on the theme in more ways than one depending on what the work is about and whether the person is a friend or new customer, or whatever. ... something like:
"As you can see, we are expanding steadily in our new market .... (whatever) ... and I am eagerly looking forward to the opportunity of working closely with you in developing the new plans we discussed last week."
Just my thoughts.
"with you" is a prepositional phrase and the 'you' is the object of the preposition there. It is a pronoun, but that is just fine -- it is simply taking the place of the noun.
I do think I would have changed a little of the grammar, though, to "I look forward to the opportunity of working with you," (if you know that opportunity is coming up) or "I look forward to an opportunity to work with you" (if you would like that opportunity to present itself in the future). Your sentence above isn't bad, just a tiny bit awkward in the middle.
And your sentence--"I look forward to the opportunity to work with you"--is absolutely grammatical. I will confess to have used it a few times myself.
There is very little prohibition against ending a sentence with anything--even the 'rule' against ending a sentence with a preposition is beginning to fade away.