How can I create a custom hierarchy to support Lean UX?

[Deleted user]

We're moving to a Lean UX style of working, and, for tracking purposes, we need to have Jira projects restricted to 3 issue types:

- Problem Statement

- Hypothesis

- Experiment

...where Hypothesis issues have a link field linking to a Problem Statement, and an Experiment has a link to a Hypothesis issue. (We also need to attach git commits to Experiments, but I think we know how to do that...)

I'm struggling how to do this. I've managed to create a project with just those issue types, but I can't see how to create the two link (custom?) fields, and how to create the screens that they display when you create an issue of that type.

Any ideas? Ta in advance...