I would advise to leave the night time bottles for the moment as they have often a soothing effect . Just focus on the daytime drinks from a cup.

If it’s just a bedtime bottle, it’s not that much of a drama is it? He’ll pretty much wean himself when he’s ready

How old is your son?? Try giving him a drink in a sippee or plastic glass before he goes to bed. Now the weather is warmer give it to him reasonably cold. It is better to give him a drink than have him waking up in the night wanting a drink.

I never gave my daughter a bottle in the first place (except once with chicken soup when she had a cold) so my answer doesn’t come from experience. I would substitute the bottle with a stuffed toy, give it to him every time he is going to sleep (in the daytime too). He might switch his need for a bottle to the toy. Explain that this is his special go to sleep buddy. Take the bottle after he goes to sleep to start with and when he wakes up cuddle him and the toy til he sleeps again. Might take a while. Good luck When he gets older you can then try and separate him from the toy lol

Just keep on persevering. It may take awhile but don’t go backwards. Keep strong as hard as it is and he will get used to it eventually.