@ocelot60- I think that you should try an Emery board that has a coarse finish. While not being as harsh as a metal nail file, a coarse Emery board is good for nails that are on the thin side yet need a lot of filing.
Another option that may work for you is a crystal nail file. This type of file has a finish that is actually similar to some types of Emery boards. A crystal nail file is also good for all types of nails, including thin nails. It is also a good tool for doing a lot of filing on nails, because it gently shortens and shapes them. I think that a crystal nail file has a finish that lasts longer than that of most Emery boards.