The more knowledge I acquire, the more I can discern from every record I’ve found so far. I passed most of my grandmother’s old photos over at first, gleaning no useful hints from them. Silly me!
Although it is impossible to discern which of these two the patch is, it was quite likely one of the two pictured above. The unit I know he was a part of, the 7566 LS Co, was indeed a Latvian unit.
The other insignia that stands out is the triangular one above the flower. It could be one of these, or a variation:
Karlis’ appears to be sideways though. I havent found a sideways triangle pictured anywhere yet!