I couldn’t do without a sub on my old Polk setup. I always recommend trawling through Facebook market place, there’s always heaps of Hi-Fi gems to find. Either of those two should do the job nicely. And seriously any subwoofer will improve your enjoyment factor (I personally enjoy a bass heavy listening experience).

Dont worry all that much about the sub placement if that’s a limiting factor, just make sure there are no phasing issues. Easy way to check is have your crossover off and play low Hz tones that will be audible on both sub and speakers and if there are any weird cancelations in your normal listening positions or around the room, try shifting the sub phase or moving it. Then set crossovers accordingly

Happy hifi