t5 will work fine.
Just buy it and plug it in.
Use Disk Utility to ERASE it before you do anything else.
If you're using Mojave or Catalina, erase to APFS, GUID partition format.
If you're using High Sierra or earlier, erase to Mac OS extended with journaling enabled, GUID partition format.
If you buy an SSD that is large enough to hold everything that's on the internal drive, you can use either CarbonCopyCloner or SuperDuper to just "clone the drive over" from the internal to the SSD.
Then, go to the startup disk pref pane and set the external to be the new boot drive.
This is not difficult.
You will get read speeds of 420-430MBps using an external USB3 boot SSD.