Okay, so I'm still on the quest for the best CD solution for DS. Thanks to some suggestions here, I've revisited fitteds and prefolds and cloth/fleece and lo, his skin DOES look better. I'm not sure what's changed (or whether he could have been in fitteds all along and it was the cover that was the problem - argh!).
So at home, I have him in a fitted or prefold and either fleece pants or a wool soaker combined with EC. He still gets a bit red, but he's lost the rash in his leg creases and on his buttocks. Yay! I'm fine with our home stash in terms of covers.
For going out though, I'm apprehensive about using fleece/wool. We live rural, so any car trip is at least 30 minutes - that's a lot of compression for fleece and wool. Is there such a thing as a cover that doesn't have exposed PUL AND has a material that doesn't get wet? Flip covers aren't working, SWWs have given him the burning rash. I want something very breathable, but I'm not sure if a non-PUL, non-wool or fleece cover exists. I can use a pocket when we're out, but if there's another option I'd like to explore it.
Bonus prefold question: he's in Premium sized prefolds right now. I use a newspaper fold, and have to fan out the top to get it to meet the back - it's beginning to be a little tricky to get them around him properly. Are toddler-sized prefolds much bigger? And is it even worth getting any or am I going to start cursing prefolds soon anyway because of toddler wriggles? (i.e., should I be on the lookout for sales on fitteds?)
Many thanks for any thoughts!