Totally Baffled M.2?

[WoZZeR]

Hi guys

I am going to soup up my Christmas Present (Raspberry Pi 4) with an external SSD via the USB 3 ports.

Tinier is better and not blocking the ports as they are all next to each other is essential.

I thought M.2 would be the way to go but the nomenclature on the drives themselves and the 'pendrive' cases is baffling.

In short what SSD am I looking for?

 

[WoZZeR]

Cheers for the replies.

The James Chambers link is excellent, it looks like I should opt for a low power NVMe drive like the WD Blue to keep to the Pi Power Supply.