If you want to use wool but want 'sewn' covers rather than knitted, the Sugarpeas covers are fantastic. They are not gussetted, but are side snapping so you can adjust the legs and waist independently. They also do Maldon Mills fleece covers.

Maz's fleece covers are awesome (and probably so are her minky ones but I can't speak from experience yet).

The gusseted PUL covers that I used are Thirsties, I liked them a lot. I found the Tots Bots covers to be a really odd fit on E, they seem really wide (in the crotch and body). Other people love them but I have only started using them recently (and as 'backup' covers), I would have really doubted their ability to contain a poosplosion, even with the gussets. Nowhere near a snug enough fit.