I found a 2TB PCI-e 2242 M.2 SSD made by Sabrent on Amazon; it was $259. I bought it, and just got it, today. I installed it (didn't seem to have any fitment issues whatsoever), and it's working perfectly. It was detected in the BIOS/UEFI and in Windows 10 without any problems, although I did reformat it when I first installed it, changing it from MBR to GPT, because there was initially 64GB of unallocated space. After formatting, the drive has one partition which utilizes the entire free space on the drive.
I'm not a gamer; I buy gaming laptops because I want a desktop replacement, and gaming laptops typically have a lot of "horsepower under the hood", so maybe I won't really have to worry about insufficient cooling (let's hope!).