V.S.
If you are having a hard time deciding whether or not to wean, that tells me that you don't feel totally comfortable with the idea. Go with that instinct and continue to nurse your little one. It's so good for both of you on so many levels. A few questions: do you have a good pump? Also, do you have time throughout your day to pump at least twice? That will help with the pain and provide you with extra milk to send to his day-care and use when he starts eating solids. I mixed breast milk with my boys' cereal when they started taking it. It won't take long for your body to adjust to a pumping schedule. I worked full-time when my boys were babies and was able to pump at work. My youngest boy never had to have formula because I was able to keep up with his demand and had plenty of milk stored up for his sitter.
However, if pumping is not convenient for you throughout the day, you can certainly adapt your son to nurse when he's with you and formula when he's not. With my first son, I was rather inexperienced with pumping and had a very difficult time producing enough milk to keep up with his demand. I started buying formula for the day-care and continued to nurse him when we were together. This worked out fine...he adjusted to the switch and so did my body.
I'm a really passionate advocate for breastfeeding, but also for the working mom. I know, from experience, how difficult this can be. I hope you find something that works for both of you! Good luck!