Hi,
Having a "no" variant, as you say in your message, is what most people do.
If you want to add a "no" default choice to your options without having to add a "non" variant, then you can add an entry with the namekey "add_no_to_options" and the value "1" in the table "hikashop_config" via your phpmyadmin.
That will add the no to all the options.
If you want to add it to only some options, then you would have to edit the file "option" of the view "product" via the menu Display>Views and change the line:
if($this->config->get('add_no_to_options', 0) && $selectionMethod != 'check') {
for your own custom condition (based for example on the value of a custom product field set in each option).