I see nothing incompatible with the Catholic Faith in what you are suggesting. It would be for you like a mental equivalent to Pilates and non-religious Yoga, am I right?
Also, seeking a purely “natural rest” for the mind, in which it has found a serenity from disturbing thoughts, is not disapproved of even in the Christian mystical tradition. It isn’t seen as beneficial spiritually either, of course when compared with supernatural rest found in contemplative prayer, nonetheless one of our greatest contemplatives, Blessed Jan van Ruysbroeck concedes:
As you can see, what Ruysbroeck was describing in the 14th century is a practice basically akin to the “mindfulness meditation” you are referring to here. There is nothing sinful about it, nothing virtuous either, its simply available to everyone naturally who strives for it - and as he says above it is satisfying for an individual to experience the fruits of, such as reducing stress, anxiety and so forth.
One thing I would say though is that “meditation” for us Catholics refers to discursive prayer focused, for example, on sacred images and mysteries of the faith such as the Passion of Christ. I would therefore, generally speaking, not use the word “meditation” to refer to a practice which is not “meditation” for us, if you know what I mean.
But on your mindfulness practice