You will need enough diapers to change your older baby 6-10 times a day. Most older babies are not pooping as much as a newborn so you will need about 2-4 covers each day when you use a fitted diaper or 3-6 when you use a prefold diaper.
At this age your baby may start to develop a different shape. You may find that a cover that fit really well before may not work as well in a larger size. If you have never used cloth before or are having a hard time finding a cover that fits, the Bummis Super or Thirsties covers fits most kids pretty well.
A nighttime diaper may be helpful as your baby begins to sleep through the night (or at least sleep a bit longer). A pocket diaper with a premium prefold or hemp prefold along with the micro insert will do the job.
At about 9-10 months, if you are feeding your baby during the night, you may never find a diaper that will last all night long without being changed (you may want to try a hemp prefold diaper before you give up). You will need to change your baby's diaper during the night until s/he stops drinking during the night.