Hi, I am also 16w pg, but I cannot stand sleeping on my back.
Probably because I am a bigger person.
As far as sleeping on your back, I wouldn't really think twice about it at this stage. If it was comfortable, then I guess I would sleep no worries. If I was uncomfortable any time during my sleep, I guess I would wake up.
Please correct me if I'm completely wrong about this anyone, as I do not really know myself.
Good luck with the sleeping. I know I'm having trouble already!!
Nicky