I have tried a few different pickups and these Schatten HD-4 pickups specifically made for Hammered Dulcmers seem the best. I did some “blind comparisons” at a small outside gig recently and we tried a normal condensor microphone verse the Schatten, and the Schatten seemed to give a nicer result and no feedback.
Here are the fitting instructions. They can be retro fitted but it is much less obtrusive if I can fit while making your instrument.
Current list price is £187 plus postage,