There are lots of different directions you could go.
You could go old-school and get an external sidecar, like the A590 or HD8+. Those can use RAM to speed things up, and some folks convert the mechanical hard drives to
SCSI2SD cards and use micro SD flash instead. I used those in several of my big box amigas (no noise, almost no power draw).
But, sourcing one of those sidecars isn't easy in 2020.
Another very popular option many like is the ACA500+, which is a brand new (2018) piece of hardware that opens up a ton of options. You can read about it
here and
here. There are also several videos on YouTube that demonstrate what it can do. It's a lot more than just a hard drive option.
There is even a cool and inexpensive clear
acrylic case for it, for those in the EU.
And then, there are a ton of internal options if you don't mind popping open your case.
There's the
Classic 520, which only came out last year iirc. There's also the
Wicher 508i.
Lots of little gadgets out there like those.
Keep in mind they are also accelerators, so if you're just looking for a hard drive solution they may be offering more than you even want and typically push you to OS 2.0 and above. So it kind of depends on what you want to do, and what you actually want when you get there. Whether you just want your 500 to "be like it was" but with a modern solution for storing data, or you want to turn it into a faster machine (which
might break some of your really old games) it just depends.