Leah, sorry your message sat here for a while. I don't post very often on this site anymore, but I started this particular forum for the exact reason you stated, not knowing anyone else who had been through both.
I'm so sorry for the loss of your son and all you had been through prior. My story is similar. We adopted, ultimately twice, after 2 m/c's, IVF and the stillbirth of our daughter. Like you the idea of getting pregnant terrified me to the point that almost 1 year to the date of our daughters birth my DH got a vasectomy. We made our very firm decision to adopt while still in the L&D with my baby girl.

At that point we both knew difinitively it was our path.
Our match for our son was a mere matter of months after our DD was stillborn so YES YES YES we were very nervous and thrilled. It's something very hard to explain to people isn't it? One thing I learned through this very unique process, even after my DS was born (8.5 months from the stillbirth of my DD) is just to feel the exact way you want to feel at the exact moment you feel it. If you are scared, don't hide it. If you are happy, go with it. You
can and will be joyful and grieving simultaneously. I've done it and so have others that I've met through the years. I found the issue was mostly other people's expectations of me. Arm yourself to tell those in your inner circle, that while you may be excited and blissful about the coming birth of your baby, you are still distraught about the death of you son. They are not mutually exclusive. Same for after your new baby is born. You must let them know that you are allowed to own both emotions at the same time and there may be no rhyme or reason to when either will surface.
I really hope you have a great and understanding support system. This is pretty heavy stuff you are enduring and I hope those you lean on understand that.