Aden is an EXTREMELY heavy wetter, and I only JUST found a nighttime diaper that will work for us. She used to use a BG stuffed with both inserts, but that stopped working after a while because she peed so much.
Now we use Holden's Landing Bedbugs with thirsties covers (they are made specifiacally to be night diapers). She has a store on hyenacart, they are kind of expensive but if you think about it you only have to buy 2 or 3 depending on how often you wash. We have 4 of them and I got them all on DS on FSOT for less than retail. She also has a yahoo group that you can sign up for and put an order into the database so you don't have to "stalk" them if she doesn't have any currently on her store.
http://hyenacart.com/HoldensLanding/
Also I have heard that the Sustainablebabyish bamboo/hemp fleece fitteds are really good for night time so that is another option you might try out. You could probably find those used on DS as well, but their website is
www.sloomb.com
And it is probably time for new covers too, but it sounds like you need a diaper with more absorbancy for nighttime.