Yes the avent white soft spout sippy worked for us too weaning our lo off the bottle. She still sucks it like a bottle (curing her tongue around the spout) but its the next step to a more advanced sippy and most importantly off the bottle.
If it were me, I would start one bottle a week to stop. And I would give it JUST like you give the bottle... ie lay her back, hold her or whatever you do when she's normally drinking a bottle. I would hold out on that bottle and never go back. So once you stop the first bottle NEVER give it... and just keep slowly eliminating each bottle till they are sippy feeds.
Then I'd start sitting her up (after she's adjusted to no more bottles) and let her drink it like a big girl.
The night bottle was our hardest to wean. But once we eliminated everyone but that one, we just went cold turkey and gave the sippy for that feed. She did GREAT with it. I think its b/c she could still curl her tongue around the spout like a bottle. But its not a bottle its a sippy.
Now she's using a sippy without a long spout...
Good luck!!