What's everybody's favorite ultralight rch?
Alpine harnesses are the lightest. I use an older version black diamond couloir (the orange one) and it is my preferred harness.
Just google “alpine harness” and you will see multiple offerings.
If not using alpine, I think the Misty Mountain Gym Dandy is the easiest to setup with lineman’s belt loops and adjusts over a large range of sizes.
All that said, rch or alpine harnesses are individual choices.