I agree, you are in a hard spot.
Baby desires hit everyone at times. But the fact that your hubby would like another child also, leads me to think perhaps you should look into adoption. I know of a few families that have adopted and never looked back. They adopted babies and raised them as their own. The kids came from backgrounds where they would not have had a chance and now they had a loving family and safe home.
One key to adoption is raising the child just like the others with the exception of taking in his/her personality. So you would not force a kid to do music when he loves soccer, just because his brother plays soccer. But you also would make others treat him just like the birth child--everyone gets a christmas hug/present/stocking. ;-)
The kids I knew all grew up and they were great! The parents were glad they were able to have them in their home.
Adopting an older child is a different ball game and I definetly do not encourage that. It is rough.
So..look up some agencies and gather information about how they work, what they charge, how long their process takes, etc. Some will work with pg mothers and it is totally open. Some don't. You may need to get a lawyer to help with the paperwork and I am sure if you ask around you will be surprised at how many people have opinions, advice, and names of sources. It is just a matter of asking questions and sorting through the info.
btw my son had a lot of only children growing up and while they were great, they did miss something in the process. The ones that tell you only children are great are the parents...you don't often hear that from the kids. ;-)
Good luck,