I use them all the time, https://www.amazon.com/Aideepen-Keyboard-Atmega32U4-AU-Development-Expansion/dp/B078KDW7W1 is the current version of the board I use I think.
Yeah, then a leo stick would be your best choice, it should work for that. Actually a Digispark DIY might work for that as well, not sure. For sure if the digispark will work it will look cleaner.
EDIT: I think I found the perfect thing https://www.amazon.com/Aideepen-Keyboard-Atmega32U4-AU-Development-Expansion/dp/B078KDW7W1/ref=pd_sbs_147_1/134-6232364-0900863?_encoding=UTF8&pd_rd_i=B078KDW7W1&pd_rd_r=4c7aee47-04fc-49b6-875e-038c3bf111f9&pd_rd_w=Blqm3&pd_rd_wg=u... IT is called the beetle and should fit your needs.
EDIT again, you can also just buy the 5pin to usb as well https://www.tinkerboy.xyz/product/tinkerboy-ibm-terminal-keyboard240-degree-5-pin-din-to-usb-converter-with-soarers-converter-firmware/ PRetty much is exactly what you are looking to do, looks like they even use the same Atmega
I was looking at another version: https://www.amazon.com/Aideepen-Keyboard-Atmega32U4-AU-Development-Expansion/dp/B078KDW7W1/
On ebay there 3 different versions of same sort.