A 10x12 room is not ideal for bass reproduction, and unless you know what you're doing, a sub can often exaggerate the problem instead of cure it. If you have your heart set on new monitors, my first suggestion would be to forget about the sub for now, and put that money toward the near field monitors that appeal most to your ear and budget.
The frequency of A1 is 55 Hz. The Wavelength is 6.42 meters, or 21.06 feet.
Even with well-designed bass traps, a 21 foot wavelength radiating in a room that size is going to present a significant problem, creating room modes that can only be minimized, not cured; the laws of physics are still going to apply.
Even with the best speakers out there, an awful lot of what reaches your ears is the room, with all its reflections, modes, comb filters, doubling, boundary issues, etc.
In any case, if the object of studio monitors is to accurately hear what you're recording, you're still going to have to contend with the room and its physical limitations.
You might consider trying something like Sonarworks' room EQ system to improve the accuracy of what you're hearing in your mix position, just remember that EQ at the mix position can be wrong for the rest of the room, since there will be room modes every few feet that will exaggerate bass, or remove it, hence the peaks and valleys that show up on measurements.
In an anechoic chamber, the Neumanns can give you clean bass down to around 50 Hz, but you're in the real world where room boundaries like walls, floor and ceiling are going to contribute to significant room modes. I doubt you'll hear that bass accurately no matter how accurate the speakers are.
If it was up to me, I'd suggest keeping the monitors you have, and spending the $1000 on a good headphone amplifier (makes a big difference) and a high quality set of headphones.
I know the old saw is, 'don't mix on cans'. That was then. Today, people mix, and even master, on cans all the time with excellent results. During Covid I did music and postproduction mixes for clients like Ford for national ads with headphones, so that the clients could listen in real-time while I mixed, using the excellent platform Evercast, with good headphones I sent them. So yes, it can be done.
Glenn Schick is a very well known mastering engineer who hasn't worked with speakers since 2011. As he says, it does take an adjustment period to learn to use cans correctly, but let's face it, it will be a LOT more work learning monitors and putting together bass traps for your room that still won't really fix all that much, especially if you're doing it without the help of an acoustician. Then there's the whole problem of where to put the speakers in your treated room, doing all that experimenting. It can take months. I know, I've done it with some excellent professionally created bass traps, and once the acoustical problems were improved in my 17' x 33' room - not solved, merely minimized - I spent weeks on end moving the monitors around until the mix position sounded like some of the big studios I've worked in over the years.
All of my work gets checked and re-checked using a pair of Audeze LCD-X headphones through an SPL headphone amplifier. I've got my monitors and room sounding to the point where what I hear in the room finally sounds like the headphones, but move one foot in the room, and what I hear changes. This is not because of dispersion or sound staging from the speakers, it's because the low end bumps up against room modes at various frequencies depending on where you're listening in the room.
It never changes with the cans.
Choose wisely and you can get accurate mixes, just don't expect miracles with low frequencies in a room that isn't purpose-designed for audio (mine is treated but in the end it's just a room like most folks have). Hopefully all this blah-blah-blah from me helps rather than confuses!