It's hard. I am in family ministries, and know very well that you are so far from alone. I also have a twenty month old who still has terrible separation anxiety, and so my dw has the same kind of struggles when she brings him to church and I am working.
I have seen different things work for different families in different settings. It depends partly on your kido, partly on your family, and partly on the culture of your church.
What is the culture of your congregation like when it comes to kids and worship? What is the sanctuary space like? We have a lot of families in the congregation I am serving who bring their wee ones to worship with them. Many congregations have a tolerance for low-level child-created noise, though depending on the acoustics of a particular sanctuary, this may or may not be improper considering the needs of people who have hearing loss. Some congregations also do not have difficulty with children running around a bit, especially if they stay to the back of the sanctuary.
Not in service, but I once attended as a congregant a church in which many families with young ones sat in the back with their little ones. The sanctuary was long and narrow, so the back was far from the front. This made for an easy exit if the children started to cry or whatever. The culture of the congregation was such that the children were part of a big extended church family, and everyone "parented" the children through the worship. Folks who felt strongly about hearing the full worship service without any disruptions knew to come earlier before the seats at the front overfilled. The rest of everyone would hear parts of the sermon, but also readily accepted that some parts couldn't be heard as well. For some congregations, this would be an impediment to growth, but in my experience, this strong family-focused culture helped bring in many.
Some churches have "cry rooms" where you can let your child play quietly and hear the sermon by speaker, while watching it through a window (or on closed circuit tv). It doesn't sound like this is the case for you, though.
Anyway, of course, this also depends on your kido. My ds is super, uber active. There is no way sitting in the sanctuary with us would be an option with ds (with dfd, quite possibly, though). We have had some experience with this, and maybe also because church is his second home but, he would do things like run up to the pulpit and grab the bell stored in it all while the person at the pulpit is speaking, or try to get all the (lit!) candles down, or unplug the microphone or whatever. It is just not going to work. dw often listens to the sermon on intercom speaker via the foyer, but this can be a little hard in our particular congregation because when people see you in the foyer, they often strike up conversation (I have been meaning to do some congregational education around this issue). So for dw, it is frustrating (we're working on a capital campaign to build on to the church, and dw is a huge advocate of a cry room). Parents in the congregation I am serving are always welcome to hang with their kidos in the nursery-- the whole service through if desired-- and listen to the worship over the intercom speakers which also are fed into the nursery. However, it is too loud in there to hear with adult-child interactions and kidos playing.
You may find that you have to just continue dropping him off, playing with him until he is settled, leaving (and usually there is some crying at this point...most folks acknowledge the child's feelings and still go, and usually the child settles down within a few minutes...often to come to play very happily), and then coming back when he is having a hard time. dw sometimes does this with our ds. The pager system is helpful for that, if you have an agreement with the nursery staff that they will actually page you if your kido cries for more than __ minutes and can't be consoled. It takes time, but most kids eventually come to accept that if they "need" you, you will return, and this will help them feel more secure and be able to tolerate the nursery for longer periods. But in the meantime, you may have to get used to missing a good deal of worship. And I know that is hard, especially when you make all that effort to get up and going on Sunday morning.
I know many couples trade kid duty from week to week. So every other week you would hear the sermon, while dh would take care of your child if he needed help. And then on the alternate weeks, you would tend to your child if he needed help. That way you can get your spiritual needs filled to at least some extent, as can your dh.
Having said all this, I want to say three more things. First, it is so helpful for kids to have a relationship with their church from early on. The kids in our congregation who come with their families to church pretty faithfully each week, you can just tell feel more at home here. It's like they own the place. They drag their parents around, proudly parading wherever they like. That is such a nice piece of faith development to be able to provide for your child. I encourage you to stick with it, even-- again-- if it means you don't hear much of worship at all for some months because you are busy tending to your child. Think of what you want for your family in the longterm, and just keep that in your mind. Second, I encourage you to speak with your director of religious education/faith development or family/children's ministries (or equivilant) if you think s/he will be supportive of your attachment parenting choices. Doing so might bring about some more suggestions or at least give you a better idea about what other families in the congregation are doing and what the congregation's culture is around this. Third, however, is a slightly different note. With another baby on the way, life will be changing drastically and all of your routines will be up in the air (I know this quite well, as my ds and dfd are 11 months apart in age). Your energy for going to church may diminish greatly. It's helpful to decide now whether this is a high enough priority for you to establish it as a routine and just stick with it even when Sunday mornings roll around and you aren't so sure...or to decide that you are okay with taking a break from church for a while. I have found that once families get out of the routine of going, it is very hard for them to get the momentum to come back, so it may be some time before your return if you decide to take a break. It is also helpful to have a gameplan about your approach if you are going to make it your routine to attend church. What will you do Saturday night to make sure you are ready to go even when things are rough Sunday morning? What time do you need to get up to make sure Sunday mornings go smoothly? Does your ds have to wake up with you, or can he stay sleeping while you get ready? Will you be bringing a sling to keep the younger baby with you? Will you go out to lunch afterward as a "treat" for you after a harry morning, or will you go to relatives, or what? How will you make the decision about going or not going one week if things are rough that morning? Is that decision an option for you? Will one of you still go on those weeks? Etc. Etc. I just recommend being clear ahead of time.
P.S. If you decide to take a break from church, or for weeks when you don't hear the sermon, does your congregation have tapes or CDs of the sermon available? That can be a nice thing for the ride home, or for Sunday night after the kids are asleep, or Monday morning if you wake up early, or to listen to in your car throughout the week.
I'm pro-adoption reform, but not anti-adoption.