Thanks again. You are all so helpful. I think I muddled the details of the timelines. There is more like 3.5 years left. Here is the timeline for clarification.
189 Visa Granted - Aug 2014
189 Visa Expires - Aug 2019
You are correct, it is a relatively 'young' relationship, but it is a serious one. We've lived together for over a year and plan to buy a house together, marry, children etc. The timelines for the Partner Visa do look very long, but the wait will hopefully be worth it. We shouldn't need any of the state benefits that come with the visa, as long as my partner can work we will be fine.
This sounds like it would work for us. Is it standard for the bridging visa to be granted with work rights?
This seems like it is the most stressful part that requires the most work. Getting all the paperwork and evidence in place. We will make sure we get this right. I see the guidance on the immigration site, is there any other useful posts on this forum or elsewhere that you'd recommend to help prepare the de-facto evidence?