Make sure to watch "A Mighty Wind".
It seems to me that a big ol' two-finger pizz would get the job done for you. You can get a pretty gigantic sound that way, and it's really easy on the hands.
I won't go down the string recommendation road again, since I've already beaten that one to death in these forums!

But "those strings" that I use make a much bigger sound on my bass than some others I've used. I think they would work really well for a folk application.
Sorry about the arthritis. I live in fear of stuff like that.