Yup, that's the one I found before posting. I was just hoping someone would pop up and say that this is planned for the next release of XF itself, as "Open / Close own threads" is a fairly common requirement for forums, and I try and avoid running addons that mess with core functionality where humanly possible.
The suggestion is located here. You can add a like to vote for it. But until its moved to Implemented / Resolved Suggestions, you'll have to hope for it and look in the HYS forum for Mike/Kier to announce the addition.