Your milk will dry up on it's own, doesn't take too long if baby isn't bfing at all. You WILL have to wear breast pads for while until you dry up. There's nothing to do to speed it along.
I am an absolute firm believer in feed your baby the way you want to/are comfortable with/works for your situation and I formula feed, but if you are considering combo feeding for the first month, I think that's a very good idea. Even if you only pump and add it to formula it's still beneficial, especially the colostrum you will produce in the first few days. My son wouldn't latch on at all when he was born so while still in the hospital I decided to go with formula, I did use the hospital pump to get the colostrum to add to the bottles though. My lo was on pumped bm for the first 3 weeks (she was a preemie so couldn't bf efficiantly) and then I gradually switched to formula. With her, my milk dried up pretty quickly even after pumping/bfing for those 3 weeks (I think I had to wear breast pads for like a week or so).
Either way (whether you bf for a few weeks before going back to work or not) your body will stop lactating within a few weeks once you're not bfing or pumping.
If you
do want to try bfing for that first month, I'd HIGHLY recommend taking a class at your local hospital. The one I took also gave a lot of advice to the working moms on when to introduce a bottle (I
think they sadi like 2-3 weeks, not positive though) so baby would be used to it by the time you were back to work.
Of course if you want to go with formula right from the start, that's fine also. I did a lot of research on the different US formula brands when I was getting ready to switch my lo and I'd recommend Gerber Good Start Gentle. They're all basically the same nutritionally, but the gerber ones have better ingredients (100% whey protien vs. corn syrup solids and all kinds of oils
).
I for sure recommend taking a bfing class regardless though, just so you'll be well informed since you're still sort of on the fence about what to do for the first month
Good luck