Convert a 60 fps video to a 24 (film) video - is it possible? This may not be as simple a problem as it may seem at first, so read carefully.

When I set my (Canon 60D, but this doesn't really matter at all) camera to record at 24 fps (I think it's actually 23.976 fps, but again, this shouldn't really matter), the film fps, it looks so "perfect", like any Hollywood movie. It is a bit stuttery, kind of "low fps" on the first sight, but it's exactly how it should look - a perfect film - and this is exactly what I want.

Now, the problem is, when I record at 60 fps to have a few more frames in case I need a slowmotion, the movie (when played back at 60 fps) looks too "fluid, fast", like a low-budget documentary movie or something like that.

The question: Can I record all my scenes at 60 fps and then somehow "convert" the 60 fps footage so that it looks like it was recorded at 24 fps ?

The reason: I need to record all the scenes in 60 fps, because I don't know which of them I will need in slowmotion later. I cannot record in 24 fps, but I do want the final cut to look as if it was recorded in 24.
You can, there's a lot of frame blending algorithms that will do it for you. That said, none of them is really great. All your 60fps footage will have a different look than your 24fps footage. You flat out cannot evenly go from 60fps to 24fps, there's just too little overlap in where the frames actually show up on a timeline. For frame conversions of that magnitude (24p->60i for TV, for example), the big boys have traditionally used telecine/telesync setups where they would literally film an image projected from a movie reel with a television camera.  

Consider shooting 50fps (if that's an option). It's much easier to go from 50 to 24 (drop every other frame, then drop one frame a second) than it is to do 60->24.