C.C.
I've been through this -- successfully -- three times. You don't mention if you're using expressed breastmilk or formula. If formula, then it's a double-whammy for you -- both weaning to bottle and formula. If possible (and maybe it's not due to your medical reasons), do it one at a time -- wean to the bottle with expressed breastmilk. Once your baby is comfortable taking from the bottle, then move to formula (best way is a mix of breastmilk/formula, gradually reducing the breastmilk until there is none).
I don't believe the type of bottle is a big factor. My daughters were all successfully weaned to the traditional Playtex disposables -- so either I was very lucky they all just happen to like the same bottle, or it really just isn't that relevant. But I do firmly believe that the mom can't be the one to initially do the bottle feeding. Dads can be successful as long as mom isn't in the room. Maybe it is because the baby "smells" you or she is just aware of your presence, but either way your baby recognizes you (and your breasts!) as the primary food source which is why she doesn't see the sense it taking a from a bottle from you. I was fortunate enough to have my MIL's assistance. But even then my girls initially balked at the idea even though it was breastmilk in the bottle. So they went a little hungry for about two-three days. And I don't mean they were being starved! They would take some of the bottle-fed breastmilk but then reject it. So we put it aside and didn't cave in to breastfeeding. And yes they cried and fussed, but then we would just give them the bottle again and they would drink a little before rejecting it again. So ultimately they got just about the same amount of food, but in sips throughout the day. But within a few days each of my girls finally started figuring it out and started drinking consistently from the bottle. And then I was able to feed the bottle to them.