This is a bit rambly and not sure I make much sense (I'm not normally like this- the tiredness has taken over) so proceed at your perile!!
DS, 20 weeks today hit the 4 month sleep regression bang on 16 weeks. We've had it now for 4 weeks. Complete joy. It begun with him waking every 20-40 minutes throughout the night. Mainly to feed. At the time he was EBF. I lost half a stone in the first week (sounds good but wasn't really as just drained to death!). Anyway, over past 2 weeks have introduced solids (just baby porridge) and formula last week (all on advice of HV/GP) as DS had dropped from 98th-25th centile. Sleep improved a bit from inconsolable crying every 40 minutes and needing feeding to waking 3-4 times through the night to feed BUT also waking every 40 mins/1 hour to cry until I give him his comforter. When he has this he feels it in his hands then falls asleep quickly (generally).
I guess what I'm asking advice on is, whether it's safe to leave this comforter in his cot at this age, then he might not wake to need it (it's this little blanket thing- silky on one side, fluffy on the other with a teddy bear head attached to it- strange i know!!). As at the moment I give it to him when he wakes through the night, wait for him to fall asleep and then take it away.
Also whether introducing more formula would help the sleep situation. I have struggled with breastfeeding all along. DS is uninterested in feeding, not gaining weight and will only breastfeed lying down. HOWEVER for the past week has taken a bottle of formula each evening with such enjoyment, appears to feed much more happily and contently. I have really wrestled with weaning him off the breast, feelings of guilt, and been in tears about it a lot of the time (that's me not him.) But he seems more content on the bottle.
Oh and finally- with the sleep regression, can I 'sleep train' (have bought the no cry sleep solution, though not had energy to read it yet!!) him into waking less? or do I just have to ride this phase out?
Any thoughts/help/advice much appreciated...