Yes you can add a blade SSD here’s the guide [guide|15758]
Here’s a good guide to review [https://beetstech.com/blog/apple-proprietary-ssd-ultimate-guide-to-specs-and-upgrades|The Ultimate Guide to Apple’s Proprietary SSDs]
As far as what blade SSD will work, sadly the 2012 model interface only supports a custom mSATA blade drive.
The newer PCIe/AHCI as well as the still faster PCIe/NVMe blade drives just won’t work in this system, sorry ;-{