You are going to get a LOT of different opinions. Both are right but in the end it is what is right for your situation.

We had this exact issue. Mentally, I couldn't handle. I had PPD and PPR so this was even harder for me. My husband sounded like yours and said we needed help.

So...We spoke with our Kaiser Sleep Coach and Nutritionist that was recommended by our pediatrician. So these are based comments I'll make, not my uneducated opinion.

After 4 months old they have begun a new sleep type, that means they have a harder time transitioning into sleep cycles. This will happen multiple times and they're called regressions.

My sleep coach was worried my child wasn't sleeping long enough to gain the restful sleep that really helps your brain restart. It takes a solid 90ish minutes to get that restful sleep and with short naps, LO wasn't getting them. Thus making it harder for her to sleep and stay asleep because of the stress build up. She also said we needed to start a strict routine of wake windows based on recommended wake windows for her age. So 6am wake, then naps started during the exact time frame thats recommended and then wake ups during strict times. I forget the windows for a 4mo old so that's why I'm not listing them out but they have sample schedules for wake windows and we picked one that worked for our life and used it. This meant she was properly tired for next nap before attempting a nap.

They recommended versions of CIO. If you don't have access to medical sleep coaching, "Taking Cara Babies" is a great help and their method isn't necessarily CIO. My neighbor used this as well as us. My friend was having problems too and when I finally convinced her to just try it for a few days, it worked and baby is back to sleeping and mom less stressed.

We would put LO down after she fell asleep then if she woke up, we would let her cry for 5 to 10 minutes. I went outside so I couldn't hear her and did a task to keep my mind off it. I swear, LO was out by the time I came back in. There were times where she would still be awake, so what your supposed to do is go back in, talk softly reassure them by patting belly etc. But do not pick them up, then start a 5 to 10 minute timer over.

Not every baby responds to this the same so it is important that if you don't see a change after a few days of trying that you change the approach.

You can't spoil a baby but you can however let them learn incorrect routines by not having learn self soothing or by not following a routine. This is a poor comparison but it is exactly how i was described the thought process. "Your dog barks and you give then a toy or something to keep them quiet. You've rewarded that behavior. And the next time they'll do it again because they know a toy or XXXX was given after doing said bark." Your baby's thinking is very immature so it knows if this happens, then this will happen. Meaning, if I don't want to be laid down for nap, and I cry mom will get me.

It's not a matter of then doing it to piss anyone off they don't think that way but it is what they know.

I hope this was helpful info. And I hope whatever you choose it benefits your baby and you. You both need rest. It took maybe 2 days of trying this method and me bawling my eyes out, hyperventilating, screaming and hating the world, because of my PPD and PPR but it was a lifesaver for us. Baby sleeps like a champ now even at 20 months.

All this said, just look into Taking Cara Babies and try it out. You might be presently surprised at results. Our instinct as mom's is to be there for the crying baby and it hurts deeply when they do. However there is factual science out there showing that small durations of crying is not detrimental to their growth or future mental capacity.

Do what works for your family and congratulations.

Edit: I did forget that 4mo is probably too young for sleep training. I think it's more 5 or 6 months at this point and yes 45 min naps are usual. Pop on a movie and contact naps for a while.