As I sit here pg with my fourth, it is so hard to put myself back in the place of a first time mom-to-be! And yet there is so much I would tell my first time mom-to-be self that I wish I had known…
I have breastfed all my children and they all received bottles of pumped breastmilk after I went back to work. DS was weaned to formula at 6 months; the other two never had a drop and were much healthier babies/toddlers in terms of fewer ear infections/croup/etc. So that is my experience and here is what I have to offer:
1. So many moms say they will “try” but give up at the slightest challenge. Don’t try to breastfeed. Commit to it. If you don’t commit, you are more likely to fail. I suggest setting a firm benchmark, such as “I WILL breastfeed this baby for 2 weeks come hell or high water.” I say 2 weeks because those first two weeks are often the most challenging. It’s kind of like starting a new exercise program. You buy the DVD and try it a couple of times, and your body is sore and it is hard. But if you stick with it for two weeks it starts to get a heck of a lot easier. Don’t let your baby be a dusty workout DVD.

This is way more important.
2. For at least those first two weeks, don’t worry about cleaning or cooking or anything but resting and taking care of baby and yourself. Accept help.
3. Now on to your actual question: you’ll want a wide-based nipple, slow-flow; examples are Playtex NaturalLatch nipples or Breastflow. READ THE LINKS for how to bottle-feed a breastfed baby that LLLmeg posted earlier. Best to wait 4-6 weeks to introduce the bottle at all, but I’d say no later than 1-2 weeks before you have to go back to work.
Congratulations and I hope that helps!