D.W.
I cloth diaper and I have both the Thirsties and Bummis brands of covers. Both are great but Thirsties just came out with a duo cover that will go from 18-40lbs so you would get alot of use out of it and you can always use it if you have more kids.
My 20 month old has been potty training since she was 17 months old and we are getting to the point that I'm going to do the same thing-put her in the cotton trainers and use a cloth diaper cover in case of an accident. The great thing about using something designed for cloth diapers is that it will breathe and be better for baby's skin instead of the old school plastic pants you find at wal-mart and target that don't breathe at all.