I apologize. I misunderstood that you were looking for a mesh system that would work with an existing openwrt router. Seems what you’re looking for is a mesh system that can be flashed with openwrt.
For that I can only suggest that you look at the supported hardware table and see if you can find what you need.
Editing my previous comment for my mistake.
I just started migrating my network from PFSense, a bunch of tplink switches and Aruba InstantOn APs to unifi. I’m almost done (just missing a couple of APs more and 1 more switch), and I honestly am extremely happy with the decision. The Unifi APs are not as powerful as the Arubas, but the improvements to the performance of my network more than makes up for that.