Best way to design a search feature so that it brings back a set of results by focusing on items that can be reserved via the website

I work on a website that uses a search bar to allow users to find training courses. The database mainly includes 3 types of courses, and only one of these types can be booked online.

By the minute, we look at all the different types at the same time and bring back a set of mixed results of course types with no result filtering option. Each result is "tagged" with the type that it is.

The client stated that users have difficulty finding courses that can be booked online.

I'm thinking of adding a check box next to the search bar with the label "Online only," enabled by default – but something tells me that it's not the best solution, and also that I do not think. it will make as much sense for the user as for me and the developers who build it.

I basically need to add something that says "Show me only the courses that can be booked via the site"

Another idea I've had is to add "filters" to the result set and allow users to narrow the result set according to their options.

So I wonder if anyone can share his opinion on this – and maybe offer another idea that will work better from the point of view of the user experience.