Ball for winter white?

[MzWiz0915]

What size ball would you recommend for a winter white?

I put Little Man in the ball for the first time today because he's being so playful and wont go to bed He's absolutely loving it! I keep taking him out every five mins for a break and to make sure he doesn't want to rest or go in his cage, but he just jumps back in the ball!

I gave him a ball that we bought for Sandy but she never got to use. He can maneuver it, but it seems a little big for him. He has trouble starting and stopping and seems to lose his footing occasionally.

This is the most adorable thing to watch in the morning