DS is 7.5 months, and sleeps fine on his back in his gro-bag at night. However, we had to resort to sleeping on his tummy for day-time naps (and achieved instant success when we tried it having battled for weeks to persuade him to sleep in the day!). He sleeps for a good couple of hours at a time this way but he spends the first few minutes in the cot head-banging, and 'constructing his bed' by dragging his blanket and teddy bear under his head. Not too sure if this is a comforter-type action (the blanket is usually quite soggy on the corners), or whether he would prefer a pillow. All the guidance states no pillows til they're one, but he's sort of making his own
Anyone else resorted to pillows at this age?