I had endless issues trying to get horizontal-form in bootstrap 3 to play nice with simple_form. It doesnt really seem like there is an easy way.
Enter simple_form_bootstrap3. You get alternative methods to use so instead of simple_form_for you can use horizontal_form_for
<%= horizontal_form_for @post do |f| %>
<%= f.input :name %>
<% end %>
You will have problems if you want to have horizontal and inline fields in the same form, in that case use compact_form_for and add the labels and columns manually
If anyone has a better solution or one that works easily in the regular simple_form gem I would love to hear about it