DS made the transition to a sippy cup with no big deal at 12 months. I was expecting the same for DD#1. She was the complete opposite. Like you, I tried every sippy and straw cup. She would drink water out of sippys, so I knew she could, but she clearly wanted her bottle. My Dr had said she should be off the bottle by 18 months so I was pretty stressed about it.
I finally decided to give up, that it was just not worth a fight, she would eventually get rid of her bottle. By 18 months, I think she was down to only 3 bottles a day, anyways. By 2, it was just once or twice a day I think. She used a sippy or straw cup for everything but milk. Finally, around age 2 I reintroduced milk in a sippy and she drank it no problem.
I think that if there are no other concerns about learning to drink from a sippy cup in general, or tooth decay that it's not a big deal to drink from a bottle beyond a year.
My twins turn 18 months next week and still have 3 bottles a day. I will likely try to switch to straw cups soon, as they use those for water. If they resist, I will just try again in a few months. For me it is not worth stressing about at this point.
DS - 10
DD - 8
Twin Girls - 6