I just purchased this OWC hard drive and, upon arrival, I realized that it does not come equipped for MacBook Pro thunderbolt 3 ports.

Allow me to add this to my list of evidence that "The 'C' in 'USB-C' stands for 'Cloaca.'"

That is not a Thunderbolt drive. Your ports are not necessarily Thunderbolt ports. In the case of your Mac, yes. In every other single possible situation, all bets are off. The USB-C port in my Pixel 3a is not a Thunderbolt port, but Thunderbolt uses USB-C.

In this case you have a USB 3.1 drive. All you need to do is use a USB-3B to USB-C cable, like this one.

First, is there a simple, reliable, adapter solution that I'm not aware of?

Yes. Since we're all living in the USB 3 world all you need is a cable with the right ends on it, or a USB-A to USB-C adapter, of which there are many.

Second, if not, would this hard drive work well for my needs?

If you need portability, sure, but as a bus powered drive that means it'll be siphoning off power from your laptop, which will affect battery life when not plugged in.