For the Balloon Bag, I pair a base yarn (like Cascade 220, Lamb's Pride, etc) with some sort of novelty yarn. I have used eyelash yarns, the ones with little flags like Cancun and Little Flowers, mohair combination yarns like Dune and probably others I can't recall.
I was NOT happy with furry yarns, the bag ends up looking like some reject from Sesame Street.
For Little Coco, the key I think is a good combination of the two yarns. I used Cascade 220 in the sample bags. You could use a novelty yarn/base yarn combo in just the body of the bag, and have plain base, piping and I-cord. I might do one of those for fall. I got the Cherries and Oranges Little Flowers by Crystal Palace the other day, and will have to find the perfect base yarns to go with it.