It is hard to exactly grasp what you are particularly challenged by (and, by the way, it is hard for most of us, but gets better with practice (as so many things)), but I still would think that using a metronome and tapping your foot along the metronome and then clapping (no instrument yet) various rhythms or rhythmical figures along to your steady tapping is the way forward. However, you probably need to start slow and easy to get your body into it (and your mind to start doing mentally what your foot is doing physically).
Perhaps go all the way down to 60 bpm to start off. First, clap along with the tapping, i.e. all down beats only. Then, clap the off beats while you keep tapping away those down beats. In fact, your foot does nothing but down beats (along with the metronome) as you explore slowly more complex beat patterns with the clapping. The first syncopated figure could be : One And … And… And Four (hope you get what I mean!?). Then slowly increase the bpm.
Before you know it, you’ll be clapping triplets and other neat stuff! Good luck!