Hey everyone! I got a Yamaha F335 acoustic guitar (black gloss finish, looks nice i think) and started to play with a pick. It was thin (0.50 mm) and it kept bending too much everytime i strummed the strings. It is driving me mad!!!

I am postive I am not stricking too hard or too soft, and that I am holding the pick the proper way. I belive the pick is too thin or made of bad material.
What pick would you recommend? There are a couple of materials that are avaliable for picks (that I am aware of, that is):
Nylon, Celluloid, Tortex / Delrex (Dunlop), Acetal, Ultem, Lexan
And which thickness would you recommend? (Thin, Medium, Thick, etc)
I was thinking this the Nylon or Tortex Medium by Dunlop:
Picks including Daisy Rock, National Picks, and PikCard USA
What do you think?
BTW, plz mention what pick YOU use to play YOUR acoustic. I just want to get an idea of what is popular and what isn't. Thank you so much in advance.
