You have chosen breast pumping to provide breastmilk while you are working part-time (less than 25 hrs/wk or fewer than 10-12 pumpings a week)
If this is your situation then you will need a small electric or battery-operated unit.
Pros: They are relatively inexpensive and portable. With the battery pack, you can pump anywhere, anytime.
Cons: If you want to use this pump frequently, you may find that pumping takes too long. Consider one of these for occasional use only.