I would just go cold turkey and switch him. I think it would be less confusing for him in the long run. My kids switched to the soft spout Nuby cups easiest I think b/c they were the most like bottles. Generally, my kids wouldn't drink milk from a sippy until they weren't offered any more bottles.
I got rid of the bottles around 9 or 10 months also before they were too attached to it, and it worked really well for us. I just offered the formula or milk in a sippy cup at the same time I would have given a bottle, and even rocked them while they drank just like a bottle. You can still snuggle if you want and not have to worry about breaking the bottle habit later! The older two still liked to snuggle with the sippy cup, but the youngest was nursing and going to a cup. He just pushed it away and would go to sleep - then he just got drinks at and between meals instead of before naps.