geegee,
what do you mean by soft castors? Im with gordanus on this, had a wheeled sofa and got those round discs to go under the wheels on a wooden floor, but then they made marks. I too got a mat which solved the problem.
[broken link removed] would probably be as good as anywhere else.
I went on [broken link removed] and that is what they said. A mat would be no good for me as I tend to go across the room on the chair! When you have looked at the link, please let me know.