So, once you install the latest beta firmware from Sony that unlocks the M.2 functionality, you’ll need a particular class of SSD known as a Gen 4 NVMe.
Without getting too technical, the “Gen 4” moniker just means that the SSD connects over PCI Express version 4. Not all Gen 4 SSDs will work, however, which is why Sony goes out its way to say that you’ll need something with at least 5,500MB/s of read speed.
Samsung 980 Pro
In some ways Samsung’s 980 Pro is an obvious choice — it’s a state-of-the-art Gen 4 NVMe drive capable of 7,000 / 5,000MB/s reads / writes — but you’ll need to add your own heatsink.
See at Newegg
WD_Black 1TB SN850
True to its name, this gaming SSD from Western Digital has the performance you’ll need and has a heatsink that will fit into the M.2 space. This one should be plug-and-play.
See at Newegg
Seagate FireCuda 530
The Seagate FireCuda comes with its own heatsink and fits in the M.2 bay area of the PlayStation 5. Its read speeds are high enough, and should also be plug-and-play.
See on Amazon
Sabrent Rocket NVMe 4 Plus
Note that even though they look very similar, the Sabrent Rocket 4 doesn’t quite have the performance required by the PS5, but the 4 Plus version does. For the price you’d almost certainly be better served by Samsung’s 980 Pro, but if everything is out of stock, technically this NVMe should work. You’ll also need a heatsink.