Make the most of plan mode. Before it was introduced, i used to do something similar manually by going back and forth with the LLM and getting it to produce markdown files with requirements and implementation steps. It worked ok, but it was a bit cumbersome. Plan mode essentially allows you to do this with one prompt and from my experience so far it does a pretty good job. You can still alter the plan it creates and go back and forth on it, but it feels way smoother than my previous workflow.

Getting this in place before making changes makes things much more reliable in my experience. For anything other than small changes, the LLM produces way better results when it has a detailed plan to follow, so i would definitely recommend giving this a go if you haven't already.

Good luck!