So i've built PRD, which proactively asks you questions about things you should be thinking about, and gives you options for decisions you can make. If at any point you feel the need to ask a clarifying question, you can branch the chat so your main decision thread can be used finally to generate your design doc, and step by step implementation plan.
Feedback on this would be welcome, if i find that people are willing to pay for this, ill probably build v2, which will integrate with github repos, to make getting context for building a new feature on top of an existing repo better.