bootheflyer,
I don't blame you for not trying to upgrade the internal drive in your iMac yourself. I looked at all of those videos myself and came to the same conclusion: I worried that in an effort to save money I could brick my machine.
Personally, I would strongly recommend that you consider installing a PCIE external SSD connected via Thunderbolt 3. Why?
If you upgrade internally, the speed of your SSD will be limited by the iMac's SATA III interface to 6 Gbps. Don't get me wrong, the SSD will still be much faster than the 5400 RPM HDD of your current drive, but it's probably not the fastest solution.
A PCIe 3.0x16 interface can have link speeds of to 16 Gbps (i.e. nearly 3x as fast as SATA III limit of your internal drive). The Thunderbolt 3 external interface can deliver it at full speed to your computer.
A PCIE SSD will be pricier than a comparable SATA SSD, depending on the size, roughly $100 more for a TB, last time I looked.
You'll need to buy a Thunderbolt 3 expansion solution. Here's the first one I found that looked like it might solve your problem (you need to do your own research). It's $230:
https://eshop.macsales.com/item/OWC/HELIOS3S/
Note that you will read in some places that Thunderbolt 3 and USB 3.1 are the same thing. They use the same physical connector, but USB 3.1 is much slower; Thunderbolt 3 is much faster, up to 40 Gbps (and much more expensive).
So here's a way to think about it:
- If you pay for an internal upgrade, you'll be supporting your local shop (always a good thing if they're good at what they do), but you'll probably pay a chunk of change for their labor to open up and close your iMac. The drive will be way faster than your current one, but not the fastest.
- PCIE will be the faster drive, but you'll need to purchase an expansion box and pay a bit more for the drive compared to the same capacity SATA drive. On the other hand, if you're at all handy with a screwdriver, you can assemble this yourself, so you'll be saving the cost of having the dealer open up your iMac.
Note, if you do go the PCIE/Thunderbolt 3 solution, you'll want to make the SSD your boot drive, but your current HDD will stay inside. You can either reformat it after you migrate to the SSD to use as an auxiliary drive, or keep it as an optional boot drive with an older OS (e.g. if you're on Catalina, but still need to run 32 bit software occasionally).
OWC is a good company with lots of Mac-specific support. You can certainly assemble an external PCIE solution from what they have to offer. If you want to support this dealer, you can also see if they can supply the parts you need.
Anyway, I hope this is helpful. Good luck!