You could also use a USB enclosure for an SSD and still use USB to connect. I have mirrored M.2 drives in USB enclosures that I switched to recently as I was in the same boat, no SATA ports available but wanted to get off the USB flash drives.

https://www.amazon.com/gp/product/B0788HBLDZ/

https://www.amazon.com/gp/product/B00KLTPW30/

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Edited to Add: I got some 3M Command strips to tape the enclosures to the side of the box after connecting to the USB so they don;t just hang there