Can anyone please help me identify replacement mixing valve?

I have a cast iron hydronic radiant floor heating system built about 25 years ago. After speaking with two different heating techs, I believe my mixing valve needs to be replaced. I don't have the $2k+ to spare for the job, so I am looking at changing it out myself. I was told it's a 1 1/4 " size. I don't see mixing valves that look like mine online though. Where mine (no labeling) is large and extends in the x, y, and z axis, these one's online seem compact and extend in the x and y axis. Can anyone please help me understand what part I need to replace it with.