hi there,
congrats on the new baby, and congrats on being able to nurse this long! you have a lot of support here, which is nice to see. the only thing I wanted to add was that your husband/partner can be a really integral part to this transition, especially considering that your relationship with your son is going to change when the new baby arrives, so you might as well focus on his relationship with his dad/other parent now, so that the change is not directly associated with the baby.
so, I would suggest picking either the morning or the evening ritual, and having dad (for simplicity's sake, I'm just going to assume you're married, hope that's ok) take over. often it's easier if it's the morning (kids are generally in a better mood and more flexible than at the end of the day), and so as an example, instead of you going in to cuddle and nurse in the morning, daddy can go in and say that you're sleeping, or showering, or whatever, but that he is looking forward to spending some quiet cuddle time with his little guy. you can prepare him for this change in the days preceding it, ie. "daddy's been wondering if maybe he could cuddle with you and read stories in the morning, would you like that?" really focus on how much daddy wants some time with his little guy, and how special that time will be for them. then, just follow through with it; if you're not there, he won't nurse, it's kind of that simple. he may protest, but then daddy is there to cuddle and give support. he's going to need to learn to rely on daddy anyway, since the reality is, if you plan on nursing the baby, there are going to be times when your little guy is going to want mommy, and he just can't have you, so the relationship with daddy really needs to be cultivated and supported.
after a few days of daddy doing morning, you can then address nighttime, too, in a similar way. it will suck for you to miss out on those times with him, but again, it's important for him to get used to daddy's style of cuddling and for him to start looking to daddy, since the relationship is going to change. this will be hard on you, but try to use the time to do nice things for yourself, and to focus on the baby.
and, of course, make sure that you are making up for the lost time by giving him extra attention and cuddles at other times, whenever possible. it's a hard balancing act, but it's well worth it when you're overwhelmed in those first few weeks with the new baby, and you know that your son has a stronger relationship with his dad.
good luck! it all goes by so fast, just know that kids are flexible, and all they really need is your time (I know, I know, who has time?!?!?!).