I think you’re already on the the right track because you’re just going to have to experiment. Once you figure out where your furniture can and cannot go, you already have an idea of where you want your main speakers, how far apart from each other and how far they should be from their back wall.
There is a misconception that all subs are ’omnidirectional’ only. That is not necessarily true. If you sit in your office chair and close your eyes with you main speakers turned off or unwired and play some music with only your subs you will sense where the subs are being played in your office room with your hearing whether they are coming from the left, right or center of the room with your ears alone and you will feel with your body which part of the room the tones are coming from.
Since I listen to mostly music than use my system for 4K dvd watching I have my front firing subs in the corner of the opposing walls about 4 to 5 inches from the back wall and the outside wall from the subs, if this makes any sense. This way I get a total enveloping of the bass sound in the entire room because they are in opposing corners and you have to leave room for you sub interconnects. This suits me quite well since I’m a bass head.
My subs are front firing and in the same general plane or in line with my main speakers along the same wall. In other words sitting on my couch I’m looking at my mains and subs. In my situation the mains will always be closer to each other than the subs are to each other. Some folks will put a sub directly behind their couch or chair for watching movies to feel the effects of the exploding bomb/space shuttle track rumble. But you also have to have the room for that too. I’ve even known people who didn’t have enough room to put their dual subs in opposing corners or one behind the couch stack them on top of each other, since they had the same footprint! And they actually sound damn good too!
Do you want front firing subs? Or down firing subs? Sealed, vented or ported? Here is a link for you to get a good visual idea of how forward firing, down firing, vented, ported and sealed subs look and there different sizes and price points: https://www.powersoundaudio.com/pages/subwoofers
You’ve got some decisions to make!