My baby is almost a month old. He has been sleeping in the baby rocker in the picture at night next to our bed. It is not a completely flat back - but close. He is in it for some naps and sometimes a swing for his naps. He is really only on a flat surface when he is laying down playing or having tummy time. Does anyone else use this ? Has anyone else been told this is bad for their spines or for them to sleep in? Does he need to be in a flat crib at night even this early or can he keep using the rocker for another few weeks at night? Please input !