Looking for Full Frame lenses to adapt to GFX

[Joeyd]

I know, I know it's a medium format camera, but I love the Helios m42 lenses on the GFX 50s ii and they aren't medium format lenses.

I have a Fuji GFX 50s ii that I just bought and recently bought a Mitakon 65mm lens which is built like a tank.I love the lens but it's extremely heavy for me.

Big side note is that I have nerve damage on my left arm & I've been out of photography a bit before I ended up with it. I bought the gfx50s ii with lenses without realizing just how bad the pain was going to be with the heavier lenses. The other option is that I may have to sell my 50sii which I really don't want to do. 

I'm trying to figure out what brands may have the best autofocus/lightweight glass out there to adapt to my 50s ii. I'm also trying to keep in mind with those lenses if I do have to sell the 50s ii I will have to decide wether to stay with Fuji or with another brand. I just don't know if theres a huge difference between all the lenses. Like how much autofocus matters between the lens you use, adapter and then the camera itself. Or if all it mostly relies on the adapter and camera,etc.