You might also check to see about purchasing an E+ subscription too.

I did that because of frequent trips IAH-EZE and there are always two of us and need to confirm E+ in advance (too long a flight to risk it)

I was even able to get United to confirm the 3rd seat in E+ because i am Gold AND had a E+ International subscription. SOmetimes just being nice with an agent is all it takes (not a guarantee)