Yeh, just check out the shop and buy tennis ball type, then fill the tennis balls.
As for tail length, the width doesn't have much noticeable effect on the way they spin, they'll just look a bit different, wider tails will drag a little bit more. Length has more effect- longer tails drag a lot more and tangle a lot.
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Live like there is no tomorrow,
dance like nobody is watching
and hula hoop like wiggling will save the world.
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Ralph Waldo Emerson