N.,
If he's doing well with a sippy cup already, I wouldn't worry about it. They're not really ready to give up the comfort of a bottle before a year. It still has to do with the sucking need, the bonding, the comfort. I wouldn't worry about it if I were you.
We weaned my daughter down to only the nightly bottle by the time she was a year old, so it wasn't so traumatic, for her or for us, taking it away. A little traumatic for a couple nights only, but thats all. The first night my daughter was so exhausted (just after a year old actually) that she fell asleep without the bottle, my husband and I stayed up to wash all of them. We got them all put away and the next night when she wanted her bottle, I looked at her and said well you fell asleep last night without one and now they're gone. You don't need them anymore, you're a big girl. It worked.
L.