Keep in mind that if you want to spend 100+ for a viz a ball, thats great, but just know that in a year or 2, he may be ready for a new ball, and then you will have to do it all over again.
If that is your case, fine. But if not, a simple plastic ball would be great (white dot, maxim, target zone, ETC) Even the Disney/Warner brother s balls are good, and not as expensive as a VIZ
Any performance ball by any company does not start until 10#.