I've just bought some dummys that are supposed to float from here:
http://www.kennelmate.co.uk/images/canvas-dummies-big.jpgThey are supposed to float and are made from that waterproof stuff you get over dog beds. Haven't tried them yet but they are slightly smaller than a normal dummy, although do weight 1lb. They are also a little bit softer which is what I was after. You can also get a "proper" floating dummy which is plastic but tbh, I didn't find fantastic. I did get it from turner richards but can't seem to find it on their site.
If you can wait until the Berwick meet, you can see what my dummies are like and see if they are suitable.
I've seen cockers retrieving adult pheasants, so they don't need to have really small dummies.
Helen