Maybe shoot instead in RAW+JPEG, then look at creating the HEIF versions from RAW? OP says " I can't shoot in RAW for a few unrelated reasons, and I need to shoot in HEIF in-camera." OP says he has a Windows computer; iMazing also available for Windows.
The JPEG format is a compressed one, so you’ll have less leeway when it comes time to edit. Of course, you’ll need a RAW editor such as Adobe Camera Raw or Lightroom, but that comes with Adobe’s Photographer package. It doesn’t matter what you’re shooting – RAW is the way to go. The next best option is the largest and highestpy0v.