I've got into bodging my own, in search of the perfect thumb-pick.... Herco brand, Heavy gauge , but I cut the 'pick' off just behind the "East" hole

To the stub, I super-epoxy (OR Krazy Glue) a Jim Dunlop .60mm

This gives me the grip around my thumb of an Herco Heavy, but the pick feel of a softer flatpick... I actually might go even lighter to .46mm on the next one I make.... Or cut the Herco even further back so that it's not quite so stiff.....

This set up allows me to (Once I get the gauge sorted out anyway) go from flat-picking to finger-style and back again seamlessly