Yup, this is what we did - over a nighttime disposable dipe. That was the only thing that worked. Until my MIL washed and dried the wool cover...
I've had this issue too! The cause of my son's leaks was the way we were putting on his diaper (we just bought OS bumGenius 4.0s). Besides making sure his penis his pointing down, the key for us was to make sure that the pads were laying perfectly flat and the upper band was laying perfectly flat against our babe's lower back. We use the long insert that comes with the diaper and a hemp insert that came with the smallest size of kissas organic fitted diapers. (DS grew out of the kissas before 4 months - he's our first and we hope for more kids which is why we went with the OS when we "upsized" his diapers. Wasn't about to buy a whole new set of overnight or hemp inserts! :) )
Before we figured out how to get the diapers to fit properly, we too put a wool soaker around the bG dipe for potential leaks. And when we freshly clean the sheets, the first night or two I'll put a towel down (we sleep together so I don't fear the towel bunching up and causing my babe problems).
Finally, I don't know the brand and have to run, but I do know that there's a company that manufactures pj pants that are made out of wool (or have some sort of wool component) that wicks away the moisture before it causes wet spots on the sheets or discomfort to the babe. I'd look into those if I got desperate for sure. (And I have definitely felt desperate! We have pampers for the random baaaaad night that inevitably happens every now and then...) :)
Blessed mom (11.10) and wife (5.01-met/12.07-married). HI!
My DD is a side sleeper and super soaker. The only thing that works is a GIANT fitted diaper stuffed to the hilt and either a wool or fleece cover. I was using a cover over a pocket but sometimes she'd still leak out the side. I think it's because there's no absorbency on the sides of the diaper, and if it's a big pee it doesn't soak in quickly enough even for the cover to keep it all in.
Oh & i'll also add that I like the Bububebes for a night dipe, esp. the minky ones. Put a some Sbish wool over it or a decent interlock wool & it works so great at least for us it did. We had issues before we found the right diaper as well. DS is a super soaker & has a strong sprayer to boot so finding something that's thick enough & absorbs quick enough was difficult. The diaper will be totally wet after 12hrs but the wool keeps his sheets & everything dry :)