That model came out mid 2017 so Im sure its out of warranty now.
It will take an standard 2280mm Gen 3 M.2 (3x4SS) NVMe SSD.
The brand is up to you, but I recommend one of the better brand names like Samsung, Crucial, Kingston, Sandisk, etc.
There is no limit of the capacity of the drive. There is also a Gen 4 edition now, but don't waste your money on that one. Your system wont utilize the faster speed.
IF you find one online but not sure about it, post the link and ask us if it will work.
Also I recommend you install Windows with the 2.5 inch HDD disconnected first. Once Windows is working, then reconnect the HDD. Make sure the HDD is backed up and then you can wipe it and use if for storage.
Tip: look inside and make sure the little screw is on the motherboard. If its missing, you will need to buy one.