What Encryption Should I Use for Database Fields Containing Sensitive Information?

My app has a few fields which will contain sensitive information and I’d like to encrypt them as they are written to the database.

Not being so familiar with encryption methods, I’d be interested in people’s perspectives on which method to use… here are some of the questions and situations in my mind:

1. Some data will be fixed (ish) length e.g. a key.

2. Some data will be quite variable length and could be very long, such as a notes field for a client’s personal information.

3. I’m not very clear about which of the cryptographic functions then perform the appropriate decryption, and whether some of the methods (such as Argon) cannot be decrypted from a database read.

4. How large a table column to assign for the storage.

Thoughts would be appreciated!

Best wishes,
Antony.