You might find mindfulness more easy when you focus on how citta conditions vedana, rather than how vedana conditions citta. Citta is like the horse (the effort) and vedana is like the cart (the feeling result of effort).
When noticing our pleasant or unpleasant feeling (or satisfying or unsatisfying might be better) instead of focusing on staying with it and not reacting try looking for what mental or physical activity we are making in connection with this feeling which might be conditioning the feeling (for example, tension or emotion). Now relax that activity (citta) and notice if the feeling (vedana) improves at all from unpleasant to pleasant, keep doing that until all unsatisfying feeling goes away.
That's what it means to engage the four foundations of mindfulness as a single process. Reducing the mental or physical activity (citta) that leads to unpleasant or unsatisfactory feeling (vedana) is the path to liberation from suffering (dhamma) and this all happens in the body (kaya). You could even call it the Four Noble Truths Meditation.