Aunty Biscuits caterpillar is going to be in 4ply.  Snag is apparently 4 ply is less common than it used to be so there may need to be slight compromise on the exact shade.  Granny Biscuit is a fan of it as she likes the definition it gives.  It is also good for dolls clothes as it provides more stitches for patterning.  I'm now wondering how many stitches would need to be casted on to make a jumper for Aunty Biscuit, I suspect the answer is a lot.