The curtain cording Martine mentioned is a great idea. I also thought you might like to dress it up a bit with some wide silky lace at the hem. Happy stitching.
For an organza skirt I once used a leaded cord - designed for (net) curtains - it's not too heavy and it did a great job. You can stitch it on with a zigzag stitch or just place it in the hem and fasten it in the seams.
I'm with Chris...we call them metal washers here in the States...in a pinch I have used pennies...but I think some sort of beaded trim would do the trick and look lovely, too!
When I made ball gowns back in the 70's and 80's I used metal weights. They are like little metal rings with a hole in the centre. I got them from hardware stores. I'm sure you would be able to find some sort of weight, even fishing stores might have them. Love Chris
Another idea would be some delicate beading as an adornment on the outside! Love Chris