You will be fine adding a sub. It will be helpful to read up on how to integrate the sub, as there are differing wiring and calibrating methods depending on the sub and your preferences. There also are sealed and vented sub endclosures, which are explained in the better articles.
In my bedroom system, I use my sub's crossover and it does not call attention to itself at all. The sub just extends the speaker's bottom end. My music sub is a sealed design vs bass reflex. I would be fine (and was for some time) without a sub, but once I got it set up, I enjoy and prefer it.
If you knew all this, please disregard. My intention was to help, not be a know-it-all. I'm a neophyte compared to most on here.
Best,
gary