Hello OP,
All the above suggestions are great. IMO, if you like the sound of Harbeth speakers, you might just want to stay with their bigger models (house sound) rather than moving to other brands. Just get a bigger model but used to keep cost down
But if you wish to move into other brands, highly suggest that you audition it first. Based on what you wrote, the size of the listening area is similar to what I have, (13 x 23 for me). Although I listen near field, I still believe that stand mounts can perform well. My speakers are Ls3/5a and ATC and they can perform well (loud enough) in my listening area (80 to 90 db.). For me, the perception of the big "you are there" sound is driven by Subwoofers, that your Harbeth needed. In my case, I use 2x Rel T/7x Subs, integrated (using ROON) well in my LS3/5a. AND, I Use a good amount of Room Treatment. All this creates a Synergy that makes my small speakers sound loud enough, as long as you listen near field.
If you wish to move to other brands, I have heard the MoFi Sourcepoints which sounds great and i believe as others have said above, the Tekton models ( i have not heard them)