This is a single node which can take the POSE_KEYPOINT output from the OpenPose extractor node, parse it, and return x,y,width,height bounding boxes around any elements of the OpenPose skeleton
https://github.com/hughescr/ComfyUI-OpenPose-Keypoint-Extractor
git clone https://github.com/hughescr/ComfyUI-OpenPose-Keypoint-Extractor
comfy node install comfyui-openpose-keypoint-extractor