I use a National dobro Thumbpick. Fairly tight and heavy. After sufficient practice they become 'part' of my thumb. I took the advice of my guitar guru, Dave Parker, and put the time in years ago. Like Mr. Fielding I buy them in some quantity. But when I must change picks it takes 5 minutes to adjust. I use metal Dunlop 23s or 24s. Like the thumbpick I don't notice them unless there is a problem with fit. The adjustment to the size and shape of the index and middle finger is important. But here's the trick. I turn the fingerpicks a few degrees inward towards the guitar face so that they strike the strings nearly straight on. This reduces the unwanted "steelpick" sound, rather like good bowing on the fiddle!

Cheers Fortunato