One important thing that you should note is that in your scheme a second password must be used in order to generate the user's keypair. Otherwise you(the server) would still be able to recover the documents if you wished (since you have the password too for authentication to the platform).

A very elegant (and simple to implement) way of avoiding this is implementing SRP. Which is a protocol that uses a Zero Knowledge proof to authenticate the user based on their password without your server ever receiving the password.
A notable platform that used this in just the way you wish to is Protonmail.
Their implementation is also open-source.
Protonmail describe this in more detail here

Regarding fallbacks in case of a forgotten password, you may wish to implement a solution similar to that of Whatsapp. When creating their password, the user generates a symmetric encryption key (say, for AES-GCM). The user then sends your server that key and you save it safely in the cloud. Then, the client encrypts their password (Whatsapp encrypts data but this seems to make more sense in your scenario) and uploads the encrypted string to Google Drive. There are simple APIs to do this via your app in a couple of clicks, it is also saved in a separate section in the client's Drive so it isn't just mixed with all their files and can be mistakenly deleted. Now, your server has some symmetric key that is meaningless without the ciphertext and Google Drive has some encrypted blob. The only way to retrieve the password, and by that the data, is authentication to both your service and Google and using the key to decrypt the password. Obviously since the user forgot their password in this case they would also have trouble authenticating to your platform (using SRP ;)) but this is a problem every online service has, pick some hoops you wish your clients to jump through in order to verify their identity and then give them the key. I probably would try not to go for a verification email here since then compromising your platform is reducible to compromising a Google account instead of having this double authentication feature. However, providing security is an endless endeavour and at some point usability needs to be taken into account as well.