All you really need is a USB3 SSD.
It doesn't have to be Samsung, just about any one you buy will give the same results and speeds.
Just make sure it's USB3 and that it's an SSD (and NOT a platter-based drive!).
Once you have it, you need to do a few things:
1. Connect it to the Mac
2. Open disk utiity
3. Go to the "view" menu and choose "show all devices" (VERY important step).
4. Now you can see the "physical drive" on the left in disk utility.
5. Click on it ONE time to select it
6. ERASE IT to APFS with GUID partition format
7. Now you can quit disk utility. The SSD will be mounted on the desktop. It's "empty", waiting for you to put something on it.
Next:
a. Download CarbonCopyCloner from here:
Carbon Copy Cloner - Download
CCC is FREE to use for 30 days -- this will cost you nothing.
b. Open CCC and get to the main screen
c. Accept all the CCC default settings for now
d. Put your source drive (internal drive) on the left.
e. Put your target drive (the SSD) in the middle
f. Ignore the box on the right (scheduling) -- you don't need it
g. Click the "clone" button and follow through.
h. The cloning will take a while. CCC will put an exact copy of the contents of your internal drive onto the SSD
i. When done, quit CCC
Finally:
1. Open the startup disk preference pane
2. Click the lock and enter your password
3. Click the icon for the SSD to set it as the "new boot drive"
4. Close system preferences and reboot.
That's it.
You should now boot from the SSD -- should be faster.
When you get to the finder, go to "about this Mac" and be sure that you ARE booted from the SSD...