worriedmum100 - Your situation is different from the OP (and most others on the thread) because your DS is 4 months.
At 6 months old most of the issues here are about extending daytime naps. In your case most of your issues are to do with leaving the fourth trimester - sleep issues dealt with in a different way.
Somewhere around 12-16 weeks baby leaves the newborn phase and two key things happen - significant increased calorific need & sleep becomes active (you/baby have to work to get baby to sleep) rather than passive.
Most issues this age are solved with more milk or more/better quality sleep
More Milk
I paid attention to my DDs milk intake at this time in a way I never did with my elder three, because I knew this change was coming. DD's milk intake went up by 25% - that is a massive amount. She had both bigger bottles and more frequent bottles than in the newborn phase.
8oz feeds (you mention) are massive. Also they must be very infrequent if only 4 a day. Many babies will take in more calories overall by having smaller, more frequent feeds. This is especially helpful to be able to calorie load in the daytime - knowing she gets all her calories in the daytime so none are needed at night.
At 4 months we were making 8 5oz bottles (they weren't being fully drained). She was fed every two hours (ish) so say 7am, 9am, 11am, 1pm, 3pm, 5pm, 7pm, 11pm.
More Sleep
As a newborn sleep is easy. Like when in the womb, as long as all needs are met then baby will sleep - its a passive state. Once bay leaves the newborn state, sleep cycles start to develop and the act of getting to sleep becomes active - requires work. Likewise the act of staying asleep through the brief wake up on one sleep cycle into the next sleep cycle becomes active too.
Now is when you need to set in place mechanisms to help the baby sleep. Many parents get into a mess here because they expect that their baby should be able to go to sleep independently (they can't).
Realistic long term expectations will help you formulate a plan of action.
- Children don't have the emotional development to sleep like an adult (tired, lie down, close eyes, relax, sleep) until school age. Until then babies need some form of mechanism to provide comfort and security to go to sleep.
- There are some methods of baby soothing himself to sleep that you can teach baby, but baby is unlikely to have the physical ability to do these self-soothing things entirely alone until more like 9-12 months old. Until then you will be required in one for or another.
At 4 months your sleep focus needs to be on two key things:
(1) Getting baby used to a good quality sleep pattern
Not getting over tired, learning to know sleep signs, sleep as soon as tired, sleep as long as possible, sleep as often as needed.
Good sleep promotes better sleep, so that once baby is getting lots of good sleep, he will be easier to get to sleep and easier to stay asleep. I favour EASY (Eat, Awake, Sleep, You time) to ensure regular feeds and sleeps throughout the day. This avoids over tiredness and the predictability increases baby's sleep quality as naps become anticipated.
At 4 months I'd go for about 60-90 mins awake time between naps and expect naps of 30-45 minutes.
(2) Establishing sustainable sleep triggers
Babies usually like your presence as a form of comfort. Give this your time and presence freely for as long as baby needs it at this age. Your reassuring presence might be snuggling next to a co-sleeper cot, a hand on chest, stroking, patting, shushing. Staying, reassuring, being there, until asleep. The value in a co-sleeper cot (and no rush to get cot out of your room) is huge here.
It is easiest to give your reassuring presence by cradling baby to sleep but this isn't a helpful sustainable sleep trigger. Being 'put down to sleep' can require some hard work, but can be done in ways to still give reassurance and without distress (see above and below points)
Bouncy chair is great for teaching independent daytime sleep. It means baby is 'put down to sleep' so doesn't develop the hard to break associations alongside rocking to sleep. Baby can be foot bounced (you sat on sofa) to sleep and can easily be taught to extend naps into a second sleep cycle by gently bouncing when stirring. Easy to control and manage the manual bouncing to 'wean off' by about 6 months.
Babies like to suck, it is natural self-soothing mechanism from breastfeeding. If you don't want to breastfeed to sleep long term, then the dummy gives an independent alternate. The value in a dummy is massive because once baby can do the dummy themselves, it is entirely autonomous in the middle of the night. There will be some dummy re-insertions before then (as the OP will tell you).
Don't worry that all of these methods to get to sleep need you. Of course they do because baby can do very little for himself and it will be like that past 6 months old. Now you are in the phase of establishing longer-term good sleep habits. Expecting self-settling is what creates most problems.
Establishing good habits in terms of frequent daytime feeding and sleeping, and good getting to sleep habits will help reduce the likelihood of baby waking in the night and if he does, will give you tools (that you have thought through) to get him back to sleep.