Best recommendation is to max out your memory first.
This 16GB module is what I have in my 920+, and it works great:
https://smile.amazon.com/gp/product/B07F6N8L3S
If you still want to go m.2 cache upgrade, I went with this:
https://smile.amazon.com/gp/product/B08DK2FB7G
If you do add cache, I recommend you under-provision it (don't format the entire drive for use, just a portion of it), and use it in read-only cache mode.
I had a problem with Corsair in the past. Changed to Samsung RAM (also u/yorickdowne's recommendation) and it has been all good, I will definitely recommend it
https://www.amazon.com/Samsung-PC4-21300-2666MHZ-SODIMM-laptop/dp/B07F6N8L3S