Rather than cheap polyester felt (which is about all you can find these days) I've found following my wife to her favourite fabric stores and hunting around for 100% wool Melton coating material fills the bill. Nice strong, beautiful napped material in lots of subdued colours, just like you would find in a best English gun case. If your going to do a nice job, spend ~ $40 and have it look and work great.
Lots of talk about using pool table material, but that be even pricier, harder to find by the yard, and it's thinner material.