I'm working on weaning my son from the bottle (11 1/2 months old), but ....?

Both of my children were off the bottle by 1. You are doing the right thing starting now. And I agree with the other woman I used the Nubby and it worked great for my daughter. You may have to try a bunch of different cups or a straw sippy cup, but it can be done. I introduced the cup several times a day with my daughter and it finally worked after a couple of weeks. Don't wait too long b/c by 15 months they already have that attachment and it will be really hard to wean.