can subwoofers make things worse?

I tried 5 different subwoofers, 4 of them made an absolute mess, also in a small room. It's very hard to get it right, if you have limited space and options. I am still better off when I turn off my sub.

The quality of sound with or without a subwoofer is a matter of both execution and personal preference.  Even in very rooms, with unlimited budget and no placement limitations, some people prefer not having subwoofers.  I usually prefer not having a subwoofer because I do not prioritize having ultra deep bass and prefer "fast" and clear sounding bass that is well integrated with the rest of the sound  i also don't want the temptation to fiddle with the bass balance for different recordings.  A local dealer who makes custom speaker systems refuses to utilize subwoofers.  Even in some systems he makes with twin 18" woofers per channel, the bass response is flat to just 35 hz or so because other aspects than ultra deep bass are being prioritized.

I own the SVS Micro. That is your best bet.

Of course anything can make your sound worse if you don't know what you're doing

 But the SVS has a good Bluetooth app that lets you dial it in at your listening position

I have two REL T/5x subs I just purchased. I also have a small listening space (12x9 or something close to that). They were easy to integrate and they make everything sound so much better. Soundstage, imaging, musicality, all better, not to mention the increased bass response that, I think, is outstanding. They are fast and tight which is the sound I was looking for. Integration is easy even though there is no app to help.  They connect at speaker level with Neutrik Speakon connectors which, I think, makes integration easy and matches the input to both speaker and sub.  I would highly recommend getting two. I love the RELs but others like the SVS and the KEF. The T/5x doesn’t go as low as the other two but I get very good in room response from them. Two of the RELs are about the price of the KEF as well.

A sub shouldn’t detract if it’s setup well, and isn’t total junk. Depending on how you configurate it and the type of filters used, some subs offer a high pass filter to keep the lows out of your main speakers that theoretically could detract a bit, but it's easy enough to avoid by skipping the option of using that HP filter.

A lot of subs I’ve heard simply have the low pass crossover frequency set too high, and even more simply turn the gain up too loud relative to the mains, which can muddy upper bass/lower mids (including some vocals) and contribute to boominess. I don’t run my mains through most HP filters of a sub, and typically run them full range. Then set the sub at it’s lowest low pass crossover frequency (~40-50hz), and turn it up the gain just enough so I can barely hear it on bass heavy passages. IMO and in my setup, it’s better to use the sub to augment the bass I already have, and not feature the sub. Different playback volume levels might require some minor adjustment of the sub’s gain up or down, but it’s a matter of preference.

Room placement of the sub is also a significant factor....you’re gonna have to just experiment and see what works best in your room and to your tastes. Running two subs to help reduce room nodes is typically preferred over 1, makes placement less critical, but obviously doubles the locations you need to find.

Haven’t played with enough new subs to really recommend any of the good ones. My Dayton SUB1200 was fine for the price, but my old Definitive Technology PF1500 sounds better to me.

Good luck!