I've got one from Trek that is ideal. Folds up into almost nothing, and has a large covered vent in the back. Pit zips would have been welcome. Wash separately by hand. The color ran like crazy. I got one size larger than needed to allow for a sweater or light jacket underneath.
Pearl had something very similar on the shelf at about the same price of $50.00. I forget why I went with Trek.
Some people are like a Slinky ... not really good for anything, but you still can't help but smile when you shove them down the stairs.