The last lot of supers I made were cut out for me, but this time I made my own pattern. Since I don't have any kids around to try them on, they may be a little on the big side, but it is based on the size of the original commercial version so it can't be that far off. Looking at the previous ones, they fit the same on the chair, so I'm guessing they are very similar in size... Might reduce it down just a little bit for next time, just to be safe :)
http://danaspageofstuff.blogspot.com.au/2015/02/more-mini-supers.html