Dear Mirandahope,
My DS is the exact same way, only he is 6 mo. However, I have (through another list in Northern VA) made friends with a woman whose 15 mo. was the same way. He would nurse only laying down....then she bought the Ergo, and it did wonders for her, mainly because DS could nurse upright.
She recommended it to me, and it has worked every so often. I mostly use it when I know I need to be out of the house for longer periods. I keep him in it, and try to stay in the same area I will nurse him for a while so he can get a good look at his surroundings and feel comfortable. Then, when he's done checking it out, he usually leans his head forward and nurses, then usually falls asleep.
Sounds like alot, but it has worked when I need a break out of the house, and it has worked wonders at the airports. You kind of have to lift your boob up a little, but its really not as much of a hassle as it sounds. Plus, it is actually a pretty discreet way to nurse.
I know its tough. Some days I just want to toss it all and get the bottle for good. And other days I swear that darn Ergo baby carrier is a straight jacket for me. But, I'm determined to nurse until at least a year and then reevaluate our nursing relationship then.
OH - did I mention that the woman with the 15 mo. also told me that nursing got much easier for her around 10-11 months? Her DS started nursing in the cradle hold and for comfort then...she attributes it to him being bigger. But she also told me the other day he still likes to hop in the Ergo on her and nurse there too

ps - forgot to add that I also have overactive letdown and nothing on Kelly helped me. I love LLL meetings too, but that didn't help either, only made me feel worse when I couldn't nurse my baby but everyone else was casually nursing their beauties in the cradle hold (argh). The encouragement was nice, but sometimes that only goes so far.