add checkbox with simple_form without association with model?

You can add a custom attribute to the model:

class Resource < ActiveRecord::Base
  attr_accessor :custom_field
end

Then use this field as block:

= f.input :custom_field, :label => false do 
  = check_box_tag :some_name

Try to find “Wrapping Rails Form Helpers” in their documentation https://github.com/plataformatec/simple_form