I would start with having my Arduboy2 library installed in the IDE. You could then create your own library using Arduboy2’s ArduobyCore class as a base:
class ArduboyTextOnly : public Arduboy2Core
If you want your library to have the capabilities of the standard Arduino print functions, you could include Print and provide a write() function.
class ArduboyTextOnly : pubic Print, public Arduboy2Core
By basing on Arduboy2Core you won’t include the screen buffer. The screen buffer is defined in the Arduboy2Base class, which you aren’t using.
You can then init the display by calling boot().
Your class would provide the text buffer and the function(s) required to render its contents to the display. You wouldn’t use paintScreen() because it requires a pointer to a 1024 byte graphic buffer.
You have to write data to the display in bytes, each of which represents a vertical column of 8 pixels. For this you could use paint8Pixels(). If you always write an entire screen of 1024 bytes, that’s probably all you need.
If you want to get fancy and write only partial areas of the screen, you could use LCDCommandMode(), LCDDataMode() and sendLCDCommand(). Or for more efficiency you could go lower and use SPI functions directly, similar to the RAM version of paintScreen(), or even directly control of the SPI controller, like the PROGMEM version of paintScreen().
You may wish look at drawChar(), and other functions in the Arduboy2 class, as templates for the function(s) in your library.
Documentation for controlling the display is here: