I know that all the "experts" say stuff. And for good reason. BUT they do not know YOUR child. So I always take what everyone else says with a grain of salt. If it will work for us, then we do it. If it doesn't work for us, we don't do it.
My son was adopted at 3 weeks. He is now 3.5 years old. He was always a paci sucker and still is. If we let him he would have the paci in his mouth 24/7. When we first got him, I read all the books and listened to all the experts who said we needed to get rid of the paci by 6 months, 1 year, etc. The bottom line is, if that's what gives him comfort, let him have it. We've tried taking the paci from him and letting the "Paci Angels" take his paci's to other little baby boys. Then a song came on the radio that says "He gives and takes away" and my son immediately said angrily that God took away his paci's and that he was mad at God. So the paci's came back. And given our sons personality...when he is ready to let it go, he will. Just like potty training....we started at 16 months, then dropped it for a few months and started back up at age 2. Then at age 3 something clicked and overnight he was potty trained.
So now with our daughter who is 18 months. She is a thumb sucker....how in the world will I take that away???? And she still loves her bottle. She will drink from all sorts of cups and water bottles during the day. But she will only take milk from her baba. She drinks a baba in the morning and one right before bed. And if she gets up in the middle of the night, she will only take her baba of milk.
With both kids we tried all the "advice" for substituting one form of comfort for another. And with both kids, they just need their paci or their thumb and baba. Given the whole picture of life....I don't think stressing about a bottle at night is that big of a deal, KWIM? If it gives your son comfort and let's you keep your sanity...go for it. When he is ready, he will let go of the paci and bottle.
And given your son's situation...he needs all the comfort he can get. Even though these little guys are so young, they understand that things are happening and they go through the same stresses that we do. Poor thing must be so confused when you drop him off for his visits with his birthmom.....:(.
Just go with what your gut is telling you to do, even if that means ignoring what others are telling you.
Think about this:
Does your son self soothe himself to sleep if he has his paci or after he gets his bottle? Both of my kids fall asleep on their own and sleep through the night. My daughter sucks her thumb and will talk to herself for a little while and then fall asleep on her own. My son will pop his paci in his mouth, play with his toys in his bed for a little while and will fall asleep on his own. We do the whole bedtime routine...rocking, singing, reading books, etc. then they fall asleep on their own.
But if you are forcing them to be without what they use for comfort (bottles, thumb and paci are the only things my kids use for self comfort), it's like taking away whatever comforts you when you are stressed or tired.
I personally would rather have my kids be able to have some independence and self soothing techniques of their own instead of me constantly having to be the one to soothe them to sleep.
But that's my opinion.
Good luck!