A went with one of the law firms that have a lot of experience with mandamus for immigration. There are some recommendations on the first pages of this thread
https://www.canadavisa.com/canada-i...amus-with-a-firm-as-a-group-meet-here.743417/, as well as elsewhere on this forum.
It cost me a few thousand, but for me it was totally worth it. I cannot imagine still be hanging in the air for several more months, if not years.
Some people on this forum managed to file the first stage on their own, and were lucky enough that IRCC finalized their application within a month, so they didn't need to continue the process, but that seemed like a risky undertaking to me.