I'm not a big wool expert but I have liked the Aristocrats and Sugar-Peas wool covers. The Sugar-Peas come in two different weight wools, one that's apparently great for daytime. I also liked that the Sugar-Peas is already felted so I didn't have to be quite as careful when washing it.

As for the covers you're using now, have you relanolized them? Part of what makes wool waterproof (or water-resistant) is the presence of natural lanolin. But as you wash them the lanolin gradually gets washed away so you need to replace it. Wool washes usually have a small amount of lanolin so it naturally replenishes it everytime you wash. But you can also just use plain old lanolin, dissolve a small amount (like about 1/4" from the tube) in hot water and then put that in the water once you're finished washing your cover. You can use Lasinoh breast lanolin if you have some leftover that you're not using but if you buy some I'd recomend just buying some cheap stuff for the covers the Lasinoh is more expensive because it's guaranteed pure and safe for nursing). I think you can get some regular lanolin at pharmacies...

Karen.