Whoever recommended a 3 ft (1m) SMB for class was spot on. I am guessing I speak for many of us when I say the 6 ft SMB I initially brought to Fundies class flopping around in shallow water just made it more difficult for me to learn the deployment steps. I later bought a practice-sized SMB ("cute," perhaps) and practiced with that until I knew the moves. Now I own SMBs of various sizes for various environments.
As I believe others have pointed out, "harness" consists of a roll of webbing, some D-rings and a buckle, and a crotch strap. There's really not much more to it. It's generic stuff, and you can buy essentially the same thing, all roughly the same quality, from numerous sources. The economical
Dive Gear Express harness, for example, meets the requirements in every respect. Nevertheless ...
I have seen others say similar. Webbing is made in various stiffnesses/softnesses. Halcyon's is notoriously stiff. My first BP/W was DSS (no longer in business), and it came with relatively soft webbing. It felt comfortable. My second BP/W I bought second-hand, and I thought I would not like the webbing as much, but I was wrong. Even the stiffer webbing feels just fine. Indeed, the stiffness made it slightly easier to put my arm through the straps when donning. I own three sets of Halcyon BP/Ws (in addition to the old DSS) and I don't even think about this aspect anymore.