>1) You didn't miss anything, Druids are inherently unarmored due to their ability to use Wild Shape which does well with mitigating damage as listed here on page 67:  
>>•When you transform, you assume the beast's hit points and Hit Dice.  when you revert to your normal form, you return to the number of hit points you had before you transformed.  However, if you revert as a result of dropping to 0 hit points, any excess damage carries over to your normal form.  For example, if you take 10 damage in animal form and have only 1 hit point left, you revert and take 9 damage.  As long as the the excess damage doesn't reduce your normal form to 0 hit points you aren't knocked unconscious.  

>I believe in first edition druids were unable to use metal because it interfered with their magic, though I have no source for that.

>2) As far as house rules go remember **Fun is KING** in D&D.  It would be really easy to take the stats for appropriate leather armor such as Hide, add a +1 to it and call it Turtleshell armor.  I'd keep the meta information out of the player's hands, but I prefer to keep as much magic in the game as possible, and just allow my players to enjoy the world.  If you do this, **there are plenty of rules on values and ways to implement magic armor in the DMG Page 285**.