So, I live in a two story house, and I have a subwoofer. any recomendations to isolate my subwoofer from my floor to keep the room below me relatively quiet?
How much money have you got to spend & would you consider replacing the floor entirely with a new one made of solid concrete, not connected to the current walls or floor?
That is not as frivolous a question as it may seem.
Audio separation, especially at low frequencies, can only be achieved by mass & air-gapping.
You could generate a bit of an air-gap by getting the sub off the floor. Whether you rest it on egg boxes or hang it from the ceiling is only a matter of scale.
Bear in mind that not only the floor, but also the walls, will transmit sound downwards to your neighbours.
Recording & broadcast studios spend $£€ 50... 100,000 truly shaping & isolating sound.
Realistically, even with the sub a metre off the floor, unless the floor itself is solid concrete a metre thick & you also float an entire room inside a room built of dense material & also isolated from the floor & walls, then forget it.
Practically, the only solution available to most people of average income in a shared building is...
Turn it down.
I once spent several thousand pounds trying to achieve similar separation for a home studio; so I did my research & built a competent isolated room structure inside the existing room, but couldn't afford [of course] to replace the wooden floors with concrete.
The room I ended up with was in a basement & was quiet as a grave from down there. In the rest of the building, however, I could 'name that tune' from just the bassline I could still hear from the 3rd floor.
A subwoofer is primarily responsible for the reproduction and/or production of frequencies you do not as much hear as you feel them. You feel them by their effect on masses like your body. The wavelengths are comparatively long, so unless we are talking about a hall, most of the sound/wave propagation will be by pressure. The only way you can not transfer pressure is by receiving it in mass and dispersing/diverting it.
That involves measures that have significant mass and cover the majority of the floor, meaning measures requiring the approval of structural engineers.
How much is that subwoofer sound worth to you?