I use a 2 piece clear plastic thing, yes it adds bulk.
However, the one time the iphone has been out of its protector was just after new year, used it in my Bose dock for tunes.
Then put phone back in pocket and forgot case, day later I decide to go to the park with my son.
thinks to myself, must put case back on at some point, puts phone in rear pocket, as usual.
proceeds to take pics of boy in park, including a nice one by sitting on roundabout with him and spinning it round.
next time I look at phone I discover a crack in the layer under the screen, which has now spread.
the are quite flexible really!