In the olden days (and well before my time, I'll have you know) the guys that played the old archtop rhythm guitars often used fairly thick hard felt picks to give them enough volume to cut through the rest of the dance band. The picks can still be gotten at a lot of music stores and should give a fair bit of volume without the hard-edged tone associated with conventional flatpicks. If it's not what you want, you're only out a dollar!