First post for me.
Until you find something that you really like and want, why not make your own for practicing. I went to a local dollar store and bought a 14"x 18" table place mat for $1.50 (nothing there seems to cost $1.00 any more), $10 for a yard of felt at local fabric store (would probably make 6 or more mats), and $10 for a large can of spray adhesive at Home Hardware (probably will make 20 or more practice mats and also good for making double backers etc. if your need them). You have something inexpensive, can roll up for easy storage or transport, easy to replace and who cares if you forget it somewhere or someone else spills beer on it, make another one.
In the end I am sure there are some very good commercial products (such as those recommended above) which will be well worth the purchase when you are ready but for something impromptu and easy to use for practice, consider making your own.