A basic itinerary should suffice and has for my partner getting a Visa in the past. Though we had supporting documentation for at least a portion of the itinerary such as train tickets, invitation letter and booked accommodation.
Please note that how the rules are interpreted varies a great deal between the nation states that make up the Schengen area, and between the different embassies. For example the Spanish embassy in Edinburgh was notorious for demanding further details and/or interviews before granting a basic Visa that would only just cover the itinerary. We applied to the German embassy and got a her a 6 month visa with multiple entries.
Ideally find someone who has applied at the same embassy to get some information about how they are applying the rules at that site. Or failing that you might find something in google reviews pertaining to the embassy.