I was petrified to drop the bottles at 12 months. I thought, oh man what kind of major adjustments, screaming, crying, transitions will I have to go through. I was dreading it like you would not believe.
To prepare for the process, we started using a sippy at snack (water) and meals (milk). He still got the bottle too, but at least he got the hang on what a sippy cup was, and what it was there for. If your son is taking a few sips from the cup, then he may be WELL on his way to success!
At 12 months, we stopped using bottles entirely. I braced myself for great protest. There was none. I was in utter disbelief! And, we went straight to whole milk in a sippy (my homegrown logic was 'new drink, new cup', associating perhaps formula with the bottle and milk with the cup). We just made the sippy cup his only option, so if he wanted to drink he had to get it from the cup. He had no issues whatsoever.
We decided that all bottles would be gone at 12 months, which also meant that there would no longer be a bottle before bed. In order to help this process, I decided to treat his 'bedtime' routine like his 'naptime' routine. About 30-45 minutes before bed, we would put him in his pajamas and night diaper. When it was time for bed, we used his normal naptime routine and put him down (he never took a bottle before nap). Again, much to our surprise he didn't even skip a beat.
I think a lot of times we forget how resilient our children are, and forget that if we are positive about change then they'll follow our lead. After all, children will need to go through many, many changes in their routine and schedule throughout their development so teaching them to adapt and be flexible is so important. I was so wound up about the whole bottle thing and when he did so well with it, I decided I would be less uptight with later changes (such as dropping a nap).