Whoa-you need more layers I'm afraid-it sounds like you're just using 1 layer of terry and 2 layers of flannel and that's not nearly enough. I may have misunderstood though. You can still use 1 layer of terry and 1 of flannel for your diaper shell but your soaker should be at least another 4 layers of flannel (if it's the super flannel or heavier, otherwise the thinner stuf won't cut it) and another 2 layers of terry. The terry has a tendancy to get stiff over time if used in the middle and can't get washed and "beaten" well so detached terry soakers are good. I have a flannel diaper that is 2 layers terry in a detached soaker and 8 layers of flannel and while this sounds like it would be huge, it really isn't since 6 of the layers of flannel are cut down just for the soaker.
Yes, hemp cotton is the most absorbant material for diapers. But you'd still want about 4 layers of it in a diaper soaker. Again, so they get clean and dry faster it's good to put 2 or 3 layers in the soaker of the diaper and another 2 layer detached soaker. This is very absorbant. It's mostly what I use.
You can always just get 3 layers hemp cotton fleece doublers to go in what you have and that may work great for you too.
I know so many layers may sound like it would be bulky but it isn't always-it just depends on how trim you cut it and the design of the diaper.
Check out Jessica at www.diapershop.com
She has lots of great diaper making info, material advice, and more and a free pattern too!