My first suggestion in the conure family would be a green cheek. Every individual bird is going to be different and you "might" get a quiet calm sun conure, Nanday or Jenday but most generally they are more noisy and tend to be a little more nippy. The green cheek is generally calmer and much quieter than the other three mentioned. My son had a green cheek from the time he was five (always supervised until he was older) but the bird was very gentle with him and very calm (she was a little nippy to me but only when she thought I was messing with her person LOL!)
I personally find Jendays to be the loudest and most nippy in the other three common conures the Sun is usually second although can still make a great companion and the Nanday has a loud shriek but is generally not as nippy. But as I said the green cheek is "usually" much calmer and less nippy.
If you are looking for similar sized birds but don't necessarily have your heart set on a conure I would also check out some in the Poicephalus family such as the senegal or Meyers. They also tend to be quieter and can be less nippy. If you have any other specific questions I would be happy to help
