To Move the Editing Cursor

Prototyping, Usability Testing
Sometimes we need to edit the words when we are typing. On every mobile OS, there would be a solution that allows you to directly move the typing cursor with the keyboard so that you don't have to move your finger out of the keyboard area and you can still keep your pace of typing.
At the moment I was thinking of different solutions for KaiOS.
Design A
A separated button at the top-right of the keyboard area. Press the button to show the direction keys for moving the cursor. After the cursor was moved to the desired position, the user might continue to type.
That little button was almost out of sight, but users know it once they learned it.
Design B
Done some tweaks to design A. I was trying to utilize the space key. Press-and-hold the space key to show the direction keys. For the rest, there was no difference from design A.
Those direction keys were too far from the space key, and the users had to be aware of the direction keys first then moved their fingers up there.
Design C
Press-and-hold the space key took the user to another mode. In this mode, the user could only move the cursor and hit a "Done" button to go back to typing.
Moving cursor became a very focused thing, and the big buttons were comfortable to use. However, the average typing speed was obviously slower on this design than on the other two.