I have a Dutch bridge and I too am a stomach sleeper. I even made a DIY 11' double layer thinking that it would be as comfy. However, I still can not QUITE get comfortable on my stomach in it, so back to the bridge I go.
As for arm position, left arm is crooked under my head for support while right arm is crooked so my right hand is under my right shoulder. This varies as I'm an "active" sleeper... (i.e. I move a LOT).
This is the same way I sleep in my bed at home so I sleep VERY well.