For the last 4 years I've used glue-on false nails, cut to size & shape. They seem to double my volume, and give a good predictable tone. They usually stay on 3-4 days, by then they've moved forward so that a string catches under the back of them and they fly across the room and land in somebody's beer. I sometimes use a piece of scotch tape to prevent that happening. You sometimes have to scrape the glue off your real nail before you put another one on.
Cheers
Ray