How can I protect headphone jack from heavy cable?
The short nub of the L shaped jack should work nicely to avoid a large lever sticking out of your headphone jack.

I actually prefer a different approach to this problem of leverage - a flexible and much shorter adapter that bends like a tree in the wind rather than breaking as a rigid lever must do.

The Monster iCablelink adapter is high quality and very inexpensive on the internet.



As you can see there are only the two stereo pins on this adapter so you will lose any microphone (and likely any button control) so you will want to select an adapter to pass those pins through if you need microphone functionality.