What is the correct model/type SSD for an old MacBook Pro 13-inch Early 2011?

My _uncle_ has the following MacBook Pro, it according with _About This Mac_ * MacBook Pro (13-inch, Early 2011) * Processor 2.3 GHz Intel Core i5 * Memory 4 GB 1333 MHz DDR3 * Graphics Intel HD Graphics 3000 384 MB * HD - 320GB - based on HDD Furthermore, in the back of the laptop appears Model No:A1278. So far, it works in peace but is very slow. In this point is not possible do an upgrade of the macOS itself. Currently it has OS X Yosemite. Anyway - he is looking for to upgrade the hardware to try upgrade the OS itself (_first, about the RAM,it is going to be upgraded from 4GB to 16GB_). About the HD, I suggested to buy a new HD of 1TB but being SSD. What is the correct model for this Mac? I want buy one based of WD (Western Digital) - I want from that company because for other laptop I bought: * WD Blue SA510 SATA SSD * 1TB of capacity * WDS100T3B0A-00AXR0 (shown in back of the box package) So far it is fast as expected. It is: * Western Digital 1TB WD Blue SA510 SATA Internal Solid State Drive SSD - SATA III 6 Gb/s, 2.5"/7mm, Up to 560 MB/s - WDS100T3B0A But because this laptop is old, I am sure not sure about what is the correct model for this Mac. Please confirm if this model is valid, if not, please share an URL of the recommended product. My uncle should buy this HD in USA. Thanks for your understanding. **Extra Question** * If this MacOS is upgraded to 16GB and 1TB SSD, until what version would be upgraded the OS itself?