So I found this on Amazon. I think I'm just going to sacrifice my WD Blue 7200RPM drive which is 500GB and get this when I can. https://www.amazon.com/Rosewill-Aluminum-Enclosure-RX35-AT-SU-BLK/dp/B004K4TE5O/ref=pd_sbs_147_4?_encoding=UTF8&pd_rd_i=B004K4TE5O&pd_rd_r=W4G7Z65A9TT9ANSZ9VNG&pd_rd_w=Q1rez&pd_rd_wg=q9XKu&refRID=W4G7Z65A9TT9ANSZ9VNG&th=1
Best bet? Get a USB hard drive enclosure, disable USB AutoPlay (in Control Panel), plug it in, and format it.
Any cheap USB 2.0 external hard drive. They sell one at Gamestop that's ready to go for Wii U and cheap. You really don't need 1tb or more, so even a 500gb or something around that size is more than enough for lots of Wii U games. I had an old 500gb desktop drive laying around the house and used this to hook it up. Haven't had to worry about it since!
It's frustrating that Nintendo didn't put an adequate amount of storage in the system, but frankly - neither did Microsoft or Sony. I have external drives hooked up to all three. The Xbox One uses the most storage since every single disk is fully installed to the hard drive.
It is just an enclosure. You essentially make your own external hard drive by sticking a 3.5" hard drive in it. It is really easy. The best option if you already have a decent hard drive laying around.
I always recommend a fresh install if possible. You can use a free disk cloning program like Easeus Todo Backup Free to clone your 60GB partition on the new 120GB SSD. There are loads of step by step tutorials available online.
As regards clearing the HDD that you remove. Once you are able to successfully boot from the SSD, temporarily remove the 'other' HDD, put in this one, and delete this one. You can then reconnect your other HDD.
If you have extra SATA ports in your computer, you can continue to use both the HDDs for secondary storage. If not, buy an ext HDD casing and convert the formatted HDD into an external drive.
I'd recommend doing this:
Rosewill Aluminum 3.5-Inch USB 2.0 External Enclosurel + Western Digital 160GB 3.5" Hard Drive
I use a similar aluminum case with a 1TB hard drive for extra Wii U space and for XCX data packs.
So for about $40 you can have a dedicated powered hard drive for more space on your Wii U. Of course you could get any 3.5" drive for it if you wanted more space or if you have an extra one laying around. That was about the cheapest I could find on Amazon.