I've used "cheap fleece" from Walmart as a one-layer cover and it worked great! So try it out. Compression wicking is normal for fleece, of course. Of the cheap fleeces at Walmart, I think the $2+/yd stuff requires 2 layers, and the $5+/yd stuff only requires one layer. I've used a remnant (30% off) of the latter, and it works great, even overnight. I just wish I'd done my tabs better so they'd completely cover the diaper.

Anyway, 2 layers will probably work fine, and 1 layer MIGHT work, but might not. Maybe cut out a diaper cut and pin it around a fitted or prefold to try it out as one layer, and then if it leaks, you can sew it into a 2 layer cover, and if it doesn't leak, you can sew it as a one layer cover? Just an idea.
