I bought and using this one for a few months
Backbone fits easily inside, it moves a bit left and right, but not an annoying amount.
It also has space for a few more things on the top lid.
Assuming that he means a travel case, Amazon Travel Case should work. The ploopy is 5.5" * 3.5" * 1.5", so it should fit inside that with room to spare for cables and possibly storing the ball separately.