Hi -
You said,
there is no navigation available other than the bread crumb or the navigation sidebar... so it would definitely confuse many users
I'm not sure why that is a problem. That is pretty standard throughout Moodle. If the user is not familiar with the breadcrumbs and navigation menu, how do they use the other activities in Moodle? If I'm in a forum, or looking at a resource for example, the only way back to the course is through those mechanisms.
If you want to set up the questionnaire so that students can't view their responses ever, you need to follow the instructions at https://docs.moodle.org/31/en/Adding/editing_a_questionnaire#ALL_Responses_viewing.
If you do want them to be able to review their responses, but not go there after submitting, you would need to supply your own confirmation page, per the instructions at https://docs.moodle.org/31/en/Setting_up_a_questionnaire#Confirmation_URL.2Fpage.
mike