Finding suitable SSD for my MacBook Air
Your MacBook Air (13" I presume) does not use a standard SSD drive in the 2.5" form factor that many others do. Instead it uses an SSD with a bare SATA connector on the end. It looks a bit like a standard memory DIMM.

I generally buy upgrade parts for my Macs via Other World Computing. there are others that are just as good, if you prefer, but this SSD upgrade would work for your system.

I would review the installation instructions to make sure it is something you feel comfortable doing.