A good option is Vet Bed. It's soft and wicks away the moisture. So does fleece, I think. I've only been able to find the Canadian supplier of vetbed, but Patti (slavetoabunny) has linked to the US supplier at least once when I couldn't find it.
http://www.vetbed-canada.com/
Perhaps this?
http://www.palacepet.com/
I haven't heard of this exact condition that she has, but I can look into it a bit. I would think it is hereditary, based on this:
http://www.medcyclopaedia.com/library/topics/volume_iii_1/s/spondylosis_deformans.aspx
http://en.wikipedia.org/wiki/Spondylosis
We did have a post a long time ago where something like this happened to a member's bunnies, but the info he gave us was a bit incomplete. Did your vet arrive at this diagnosis from an x-ray? It seems to be a form of spinal arthritis, which I have heard of affecting bunnies and causing progressively worse pain and limited movement.
TreasuredFriend has a disabled bun, so she would have good info to help you out. I think she knows a bit about wheelchair options as well. I think she has one for Karla (her disabled girl) for run time outside? Some people put infant diapers on their bunnies to help with incontinence. Another person to talk to about this is Luvr of Wabbits and Polar Bears. Her disabled girl Monsters passed away just recently.
You may also want to join the disabled rabbits Yahoo group. I hear they are picky about who they let join (ie not people like me who don't have a disabled bun, but are just interested in rabbit health), but they are very supportive of members. I would bet they have a bunny on there with something very similar. That UK forum would also be a good place to go, since it seems one of their members has a bunny with a similar condition. Randy may have experience with this condition as well.
I'm sorry it's not good news. You've had too much tragedy lately. You're a great owner for committing to care for her. I know she can live with you comfortably for at least a little while longer, but if dealing with a chronically ill bunny is too much for you, I can understand.