Best way to design a search functionality so that it brings back a set of results with a focus on the 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.

[UPDATE]

After finding out that there will be the possibility of more options for filtering, the idea of having a checkbox is out of the question - and as explained by 0NLY777 and Mattynabib probably not the best idea in this situation anyway.

Anton Mircea's suggestion of taking a similar approach to Amazon is the route I have decided to take. At least for the initial search, and it's going to look a little bit like this...

I'll then be adding clear labels to the result list on whether a course is bookable online or not. As well as adding a sidebar with filter options on the results page.