My brother and I live in an apartment that we received from our parents, basically our parents were loving enough to give us an apartment lol so we own it
I have Genelec 8030c and I really like them, but Ive been hesitant about buying a subwoofer since I live in an apartment.
I live in the first floor and there are two floors above me. The ceiling is concrete, but the walls are drywall.
If I were to get a subwoofer with feet to separate it from the floor and keep it low volume, I wonder if other can hear or feel it.
I read of people who built concrete enclosures for subwoofers
The biggest tradeoff you will need to make is not getting a Sub that will generate a lot of infrasonic content. In a way, that kind of defeats the purpose in my book, but as I said... Tradeoffs is the name of the game.
If I were in your shoes, I would just be looking for something that can go down to the low 20Hz range to flush out the bottom end and cross it to the Monitors at around 80-90Hz. Look for sales maybe on a Monolith 10 or 12"... they happen pretty frequently and the distortion measurements show them to be pretty clean units, even the lower rated 10".
If you think you plan on moving in the next few years and want to buy something enormous, now... I would say to get a DSP module like the Flex and put a High Pass Filter on the low end. Also, avoid creating a big house curve... keep the FR flat and output under control.
Lastly, the volume control is your friend. Use it smartly and communicate with your neighbors. Good neighborly relations can bypass a lot of problems and keep them from escalating to actual complaints.
Just remember you are in a shared space and need to be mindful of what will keep the peace with those sharing walls and floors with you!
This isn't guaranteed to work, but if you want to add a Sub it is your best approach. I had a small toy Sub in an apartment years ago and never received a complaint from my downstairs neighbor. It wasn't a monster Sub and didn't have insane output capabilities. On the flip side, it did distort easily which creates it's own issues because those types of rattles and bad bass sounds are what most people complain about IME.
Good luck!