Sure you can:

https://www.amazon.com/Blue-NAND-500GB-SSD-WDS500G2B0B/dp/B073SBW3VD

https://www.amazon.com/Samsung-860-SATA-Internal-MZ-N6E1T0BW/dp/B07822Z77M

Are you sure none of your Skylake motherboard M.2 ports support NVME? I guess it's possible if it's a less expensive motherboard but it's certainly not a Skylake limitation, my old Skylake PC on a Z170 chipset motherboard has a 950 Pro NVME system drive