You need an additional opinion like a hole in the head but I have exactly the opposite problem. My audio room is really confined (8-1/2 x 12-1/2) and uses not only room treatment but multi band equalizers to null out or correct (mostly) bass... so count your blessings! I’d trade in a minute if I could.
The problem with movable walls is that they tend to resonate more than fixed ones that can be re-fortified for rigidity. Back in the day I had my share of planar speakers (Magnepans, Quads, etc.), all crying for more bass. My suggestion along with others here is a subwoofer but without any ports (or block the port) and a very low crossover point, judiciously used and keep your room open. Good luck with your choice!
The problem with movable walls is that they tend to resonate more than fixed ones that can be re-fortified for rigidity. Back in the day I had my share of planar speakers (Magnepans, Quads, etc.), all crying for more bass. My suggestion along with others here is a subwoofer but without any ports (or block the port) and a very low crossover point, judiciously used and keep your room open. Good luck with your choice!