I struggled a bit trying to obtain a keyboard setup for my US keyboards enabling me to use letters with accents. So I report my configuration for future look-ups. (Note: I use the left Window button to activate the accent feature)

This is the content of the file /etc/default/keyboard/:

XKBMODEL="pc105"
XKBLAYOUT="us"
XKBOPTIONS="compose:lwin"

BACKSPACE="guess"
XKBVARIANT=""