Am I better off just getting two 1x15 cabs instead of getting a 1x15 to add with one of my 2x10's? I really miss the fullness and warmth that you can only get with a (really good) 15 inch speaker
I read as, you have a 2 x 10 and want to add a 15. But if that doesn't work, you are willing to get a 2nd 15.
I suggest trying just that. Get the 15, play it, if it's good, done. If you don't like it, get the 2nd 15 to match. Keep the small one as a more portable rig, or sell.
You may have trouble in the bedroom. That's beside the point. Trouble with blowing up the 15, I think, unlikely. Noise ordinance violations, ear drum repair surgery, family problems, neighbor hate and rage, all more likely to happen unless you get hold of a really weak 15 or really over eq the low end. In very small rooms, phase schmaze, you 2 x 10 is already having phase issues with itself and canceling out itself in random frequencies. Well not really random, but unknown.
I say experiment, learn, live, love, hate and rebel.
Post up some wattages and models of your amp, the 2 x 10 and the 15's you are looking at if you need any recommendations on matching up for cab safety. Wear hearing protection when you crank it up.