S.M.
I had the same problem with my now 7 month old son. This is what worked for when he was 5 months and i had to go back to work. I decided to ditch the bottle all together, why try to improve on the best (breast)? We tried all sorts of sippy cups. He likes the Avent sippy cup the best. That seems to be the easiest sippy cup out of all of them. Beware or the born free, they are hard to sip from and just frustrated my son to no end.
What worked the best for us ultimately was a straw. He now drinks whatever from a straw. What we have is the foogo stainless steel thermos with the straw top. He likes it and I feel like it was an easier transition for him. It did take two or three times for him to get the hang of it, but he prefers it now. We usea combination of Avent and the foogo. FYI-the foogo sippy cup is way too heavy.
You can also start on the basics of the cup too. I would'nt even worry about the bottle, I think it's a bad habit anyway.
good luck.