Do you want a foot rest to brace against or rest your feet or do you want a bolster seat or riser?
The most simple solution would be to add a riser pad if you have room between the wheel and the seat cushion; it would be easy to make or have made. The seat you are looking for is a bolster seat and they are readily available from a number of sources at reasonable prices. Finding one that will match your decor might be a bit challenging unless you get custom colors for it, and of course, you will pay extra for it. You may be able to retrofit your seat, but the cost may not be worth the effort unless you DIY.
Last edited by Iceberg; 09-16-2013 at 10:09 AM.