Burntstump- I use Herco (blue) thumbpicks which are 10mm x 30mm and quite flexible, far better than the rather heavy, stiff Dunlops. I had to buy them from the US in quantity, if you PM me an address I'll send you two or three to try.
Cheers,
J :0)

PS in my experience it's not a good idea to have just one 'favourite' pick that you use all the time, lose or break it and you're knackered! :0)