I have heard that when they are able to lift their heads on their own, you can let them sleep on their tummies. I haven't tried it, but if your son has gas, tummy sleeping may help. Maybe you can let him nap on his tummy when you are close as a "trial" to see how he does. I also cary my son (who aslo has terrible gas and reflux) around in a sling. He absolutely loves it and it really helps!
A wonderful book that will help you help your child sleep through the night is The No Cry Sleep Solution by Elizabeth Pantly. My son was getting up every hour and after trying just a few things in that book, he's gone to being up every three or four in just a month... huge difference!!! When he does wake up, it is only to eat, then he goes right back to bed (I co-sleep, so I just lay him next to me). The whole process only take about 10 minutes. I strongly recommend not trying the cry-it-out method. There are just much more gentle ways to accomplish the same thing.
If you want to buy a sling, I bought one from Momma Trends, which is a momasource buisness. They are really affordable and well made!