The diagram is a good solution, but it really doesn't match vanilla Minecraft. To revamp the feel of MC while preserving the aesthetic while still being able to see my health, I'd love to see a health bar like in vanilla but segmented and organized by body part. Head, then body, arms, legs, feet. Perhaps as an alternative option to be turned on/off in the mod options. The body menu to heal with can be altered to be a simple bar with labels. The alternative, of course, is a more vanilla friendly aesthetic that's still a big green dude on my HUD... just not as glaring.

I would add that the healing mechanic could theoretically be made into a drag/drop system on your health bar integrated into the standard inventory, but that's a LOT of programming and fixing.

I'm not sure how this would function with resource packs, but generally I guess the textures would still be sourced from the same files, right? So that wouldn't be an issue unless you want to combine whatever extra art is made with the original bar.

Thanks. I love FirstAid as a mod that really revamps the game neatly, but my own picky taste really would love more aesthetic options.

This does sound similar to just enabling vanilla health bar with the lethal bits marked, but I think it's different enough to warrant some experimentation.