For babies to have comforters in the cot? DSs sleep has come a long way and massively improved (hes now 4m). Hes falling qsleep on the bottle at night which for now i dont care about but long term i know we will need to change. Id like to start giving him something like a comforter or specific teddy at bedtime so he starts associating it with sleep with the long term aim to get him to go to bed awake and self settle. What age is it safe to do this?