Thanks guys for your replies,
Using deer hair as in the Bomber Shrimp is a sure possibility which I will still try.
First I tried using foam, underneath a (not too thick) layer of epoxy. With the thin sheets of foam it did not work, the buoyancy is not enough to make it float. It does swirl very naturally though as it becomes about weightless. When I used a cylinder of foam (regularly used for boobies) the buoyancy was o.k. Step 2 was to simplify the pattern in order to be able to tie them fast enough but still have it looking catchy. I don't like flies on which I had to spend more time tying it then being able to fish with, it holds you down on risky casts/spots (where in general you will find the better ones) I have enclosed a picture of it, showing itís buoyancy. Now it should be possible to present the fly just above the bottom. By twitching it it will move closer to the bottom and vice versa.
Unfortunately it will take some time before I will be able to try it: sea bass, as stripers, move out of our region into The Channel during winter. As soon as I have any results I will mention it.