I've just finished experimenting with making a soft sided bead tray. This is made from vellux. You can tie the corners together to form a one inch side all around to corral the beads.
Working with vellux was a challenge, a sewing lesson I learned long ago but haven't applied in many years. I had a hard time getting the casing sewn down even. Finally I had to go online and find some tips about sewing velvet before I could figure out what I'd done wrong.
Hopefully the next bead tray will be more "perfect". I love this for my lap tray because a flat bead mat on the flat top top of the tray is always tipping and I end up having to pick up the beads from my lap, the chair and the floor.