I found Cushie Tushies way too big for her as a newborn, Baby Beehinds and anything else with a wide crotch were a bit iffy too.
For newborn poosplosions, best containment is fitted with cover, or flat/prefold with cover. I didn't worry about EC-ing until her poos had become less frequent. (At first it was 12 poos a day!) I have heard a good trick is to get a stretchy headband around baby's middle and use it to keep a prefold in place, then just flip the front out for wees. You would probably need to flip both ends out for poos... Honestly, if it's a real poosplosion, it will leak out of whatever, so you just have to deal with a certain amount of poopy clothes.
Good that bub is not due till spring - EC is much easier in warm weather, just leave them bare-bummed and watch for cues.