If you're going to use SD Ultimate Upscale, I suggest leaving the positive and negative prompts blank and going for a low denoise. I also enable Tile/Blur ControlNet when doing this.

The image in the post is upscaled 6x using SD ultimate upscale. Here is the original image upscaled only 2x using hires fix:

I used the OpenPose ControlNet model. Just used a pre processed pose I found online as the input.