Years ago a flamenco player told me he used tissue paper and shelac to strengthen his nails. No need for picks. I was also told to eat jelly cubes to harden my nails - might not work but tastes good - brewers yeast is good and try some nail hardeners - my wife buys mine to save odd looks at the till in Boots. Using a thumb pick depends on how you play. I used to use one but I changed how I play and find it better without one. I now have 2 tortoiseshell thumbpicks banned by CITES. Not used and glad it was stopped.