I think you have your ideal bird already "Kiwi". And I would suggest not getting another unless another budgie for his sake.
A cockatiel have all the attributes that you are looking for in the above post, they are very sociable, they may be small, but they have big personalities and can be very affectionate. They are a great next size up bird from the budgie. They can come out and play with the budgies, but I would not keep them in the same cadge over night together with the budgies.It's not just a talking and pretty looks. I'm looking for playfulness and bond and for interaction with all family members. For fun and companionship and affection. Id like them chatty and singing and responding back when you comunicate.
Generally a good companion that would love to spend time with us and make us laugh playing around and spending time around us when out of cage.