That's what Isolation is.
That would be the inexpensive way to do it.
So....everyone has pretty much told you that acoustic treatments won't do what you need, at least directly, and the full on, expensive room-airgap-room thing is the only way to actually isolate the sounds you're making from the outside world.
And you're using a e-drums with monitors (or PA speakers, doesn't actually matter) and your goal is to be able to feel it (which I assume means the sound kicking you in the chest) without having too much leak out. Some of that comes from the crack of drums, which can significantly be around 1k; some of it is an octave or 2 lower...some of it is flat-out sub-bass.
They're not cheap, but there are "treatment"-like things that could help with that....indirectly.
I don't think you've said how big this room is or where it is in your house, so I'll assume it's not in a basement (which you don't seem to have) and that it's a relatively normal room inside a house, rather than a freaking huge (many hundred square feet) room with huge vaulted ceilings. That is a NIGHTMARE for accurate bass and sub-bass. If you actually bother to measure it, you're probably going to find 40dB swings in nearby sub-bass frequencies....but to a great degree, the level the speakers are producing (before the room effects take 20-40dB off some of them and reinforce others) is what's escaping.
The "problem" is that below some critical frequency (in my well-treated and essentially GiK-designed room, within the constraints of what I had to work with, it's actually up around 100Hz) the sound inside the room is mostly the result of big woofers changing the air pressure inside the room, which then makes the whole room act like an acoustic drum or subwoofer cabinet. Inside the room, you can't just think of sub-bass as standing waves....it's more complex than that.
So, what I would suggest is to take advantage of return policies and at least try a 2 or 4-subwoofer setup according to these guidelines: (had to remove the link; something about spam) Search for GiK Acoustics, speaker placement 201 part 2: using subwoofers or something like that. I am not trying to get you to buy their products and neither is that article. It's about physics and subwoofer placement.
To answer some obvious questions:
Yes, you're going to have to move heavy subwoofers around to try the different options.
No, where you put them has absolutely no impact on stereo imaging.
Yes, it's a lot more power going to sub-bass....but you're taking advantage of them cancelling each other out.
No, more subwoofers does not necessarily mean louder sub-bass.
Yes, you need a tunable crossover that's more detailed than anything that comes built-in to any sub on the market....that's the complex part.
FWIW, all of my sound goes through my computer anyway, so I use 2 instances of FabFilter Pro-Q 3 for my XOs. I have 2 versions of my monitor control Reaper session...one set to "zero latency" mode for everything for low-latency monitoring, the other set to "Linear Phase - Maximum" because it sounds noticeably better, but the monitor path adds about a full second of latency...which is what I use for mastering projects because in that context the accuracy matters heaps more than the latency.
Your goal would be to even out the sub-bass response so you get the rumble/thump that you want at a lower overall volume level. Better sub-bass does generally mean that you need less overall sound, which means the room itself acting as a drum/subwoofer can be quieter from outside.
If the track is good, my system will rattle your bones and smack you in the chest at 85dB SPL....and at that level, very little leaks to outside. Some still does, but not as much. In the living room, which is much less treated and doesn't have the subs....you flat out can't get the same feeling. But to get close means the in-room level is closer to 100dB and a lot more leaks outside....because it's almost 3x louder.
It might not work. But, you can't really return construction supplies after you've used them. You can return a pile of subwoofers if they don't work for you.
I'd still look at decoupling the subs from the floor and putting your tops on stands where you want them for detailed drum sound in the playing position....and I'd probably still put bass traps in the room corners (floor to ceiling) and at the first reflection points for the drum tops from the drummer's position (assuming that's your biggest goal for the room) just so the rest of the sound is more accurate.
But...that's what I would do.
It's neither simple, nor quick. And it's not guaranteed to work. And my thoughts come mostly from a LOT of experimentation over the course of about a year building my mastering room and deciding on speakers, which obviously has different overall needs. But, that's what I would try first.
Literally none of the easy "just put this on your walls" isolation things actually work. They're like the egg-crate looking sound "treatments" that a lot of youtubers use....they do something, but it's never something you want. Unfortunately, unless you cover all of your walls with them, they're so ineffective at what they actually do accomplish, that most people don't notice and think that because they did something, it's better (literally all they do is reduce flutter echo).
So....take all that for what it's worth.
But, a bottle of whiskey every month or so is going to be cheaper than any form of "doing it right".
Thanks for feeling yourself into the situation and