justj,
Pardon me for butting in but I almost always use booster pads with my diapers. Don't select the size of booster pad based on the size of the diaper (except that it has to fit inside the internal standing leak guard)s. Rather, estimate how much additional absorbency you need. You may need to do this by trial and error.
Re size, I like to ensure that there is ample space on either side of the booster pad to leave a gutter for pee to run into the mat of the diaper itself for faster absorbency. Do note that, just as all of the rear part of your diaper usually has not been used by the time you change, the same will happen with a booster pad that is too big. For me, a size small means that I use all of the booster's capacity and don't waste any money.
Either an Abrilet Normal or a Northshore Booster in size Small would be good choices. They have very similar costs and absorbencies.
The Abena Abrilet in size Normal has an absorbency of 16 oz. It would cost $.35 per booster purchased by the package at XP Med.
NorthShore Care offers their own line of booster pads. These are the ones I normally use. They have a capacity of 15 oz. The NorthShore Booster in size small would cost $.33 per booster when purchased by the package.
Good luck and let us know how it works out for you!
--John