It is great that you are looking out for your own health and the baby. There are different studies about coffee drinking while pregnant. It is still recommended not to drink caffeine drinks: coffee, teas, sodas (Coke, Pepsi, Mountain Dew to name a few). Decaf drinks do have a minimal amount of caffeine, however, they are safer to drink. Suggest increasing your consummation of water, which is a healthy benefit. Thank you for your question.
First of all, congratulations on your pregnancy. I've read a lot about drinking coffee during pregnancy as I am currently 20 wks pregnant. Apparently, studies show that drinking coffee doesn't affect your baby as long as you don't overdose on caffeine. I usually drink one small cup in the morning (about 6-8oz) and sometimes one in the afternoon to keep myself alive at work. Keep in mind that tea and some sodas contain caffeine as well so if you consume these drinks throughout the day, it adds up. Also, decaf drinks actually do contain a small amount of caffeine too. You mentioned you drink a lot of decaf, I don't know how much is a lot...
I hope this helps. Good luck to you!