Best way to display an option that online brings back a result set with items that can be booked through the website

I'm working on a website that uses a search bar to allow users to find training courses. There are mainly 3 types of courses in the database, and only one of these types can be booked online.

At the minute we are searching through all the different types at the same time and bringing back a mixed result set of course types with no options to filter the results. Each result is "labelled" with the type that it is.

The client says that the feedback they're getting is that users are finding it difficult to find courses that can be booked online.

I'm thinking of adding a checkbox next to the search bar with a label "Bookable Online Only", that is set to on by default - but something's telling me this isn't the best solution, and also that I don't think it will make as much sense to the user as it does to me and the developers building it.

I basically need to add something that says "Only show me courses that can be booked through the website"

Another idea I have had is to add "filters" to the results set and allow users the ability to reduce the result set based on their options.

So I'm wondering if anyone can share there opinion on this - and maybe come up with another idea that will work better from a User Experience point of view.