Great advice.
I always recommend simulating treatments with pillows, cushions, and blankets. I have made some of those permanent with heavy woven wool oriental carpets. While expensive they are really beautiful and great acoustic treatments.
Go ahead, hang blankets on the side walls. You’ll be amazed.
Had Pass Labs Aleph equipment until 6 years ago when I replaced it with Devialet 400 monoblocks. Used them in a 12 x 23 x 8 shared space. Recently moved to a new house with space for a dedicated listening room and decided to return to my analog roots in an end-game way. Went preowned on the electronics and still spent a lot but the music is remarkable. A lot of credit has to go to the luxury of a dedicated room and the opportunity for abundant acoustic treatment. Did not plan it this way, but my budget turned out to be about 1/3 preamp, 1/3 amplifiers, and 1/3 room treatment. I believe the room treatment made the biggest difference. For those starting such a journey, simply taking care of the first reflections off the side walls and perhaps the floor will make an audible and likely convincing difference.