You can add numbers to pagination buttons under Theme. You can access the Theme section up the top right of the form editor.

The theme button, in the navigation bar

To add numbers as your pagination buttons, go to:

Theme → UI Elements → Pagination Buttons → Pagination Style and choose "Numbers".

Pagination Style choices

This feature is available for both Standard and Guided Mode form experience. See below the numbered pages in Guided Mode:

Numbered pages in Guided Mode