double-prefix-only

double-prefix-only is a variable defined in `double.el'.
Its value is

t

Documentation:
Non-nil means that Double mode mapping only works for prefix keys.
That is, for any key `X' in `double-map', `X' alone will be mapped
but not `C-u X' or `ESC X' since the X is not the prefix key.

You can customize this variable.