The MacBook Air you're using has a proprietary SSD interface from Apple, so you can't directly use a regular M.2 SSD from the market; you have to go through an adapter. For instance, the [link|https://www.sintech-shop.co.uk/m2-ssd-card-to-26-pin-card-for-macbookair-2012/a-10811|Sintech M.2 NGFF SSD to 26Pin Adapter|new_window=true] has a good reputation within the Mac community.
Don't forget to back up all your data before installing the new SSD. Checking [link|https://www.jakelectronics.com/|the website for information about SSDs|new_window=true] can help you make a better choice.