here bone lammellar, as far as i know its not heavy, at least compare to their metal counterpart.
from: pinterest
from:https://siberiantimes.com/science/casestudy/features/warriors-3900-year-old-suit-of-bone-armour-unearthed-in-omsk/
and technically i think it can reach high enough to cover the neck to form like a collar or to form as gorget just like this chinese han and jin lamellar armor, since wild predator usually aim that part.
from:https://weaponsandwarfare.com/2020/06/11/han-dynasty-frontier-armies/
from: https://www.artstation.com/ginkgostory
from:https://dragonsarmory.blogspot.com/2021/02/the-first-chinese-cataphracts-3.html
and tusk helmet
https://en.wikipedia.org/wiki/Boar%27s_tusk_helmet (cant upload the image so i just link it)
and technically its possible to cover the neck and overall face like this lammellar helmet from china too.
and you can cover it with boiled leather as already mention by KerrAvon2055 as a form of coat of plates or brigandine depending on how big the bone or tusk are, or a surcoat if you dont want to attached them together.
i recommend to close or fastening it from the front or side rather than in the back as shown already in the inuit armor there, so you personally can wear it without need of help.
so i personally think this can be easy to wear and can fit all.
and also ironically since we deal with non sentient monster (i assume) studded armor (as much as non-historical it is, we are dealing with fantasy monster here after all) and i mean the spiky one, think geralt spike armor (never play, watch, or read the book though), so the monster cant touch you without getting impaled by the spike, even better if you coat it with poison (just need to be careful to not get prickled yourself).
either carve the bone to become spike or use animal tusk and sharp fangs and attached it to the leather/boiled leather.
and here siberian bear hunting armor as reverence image (dont take that too literally), although tone the length a bit and not the entire body like that, though i recommend the side in the armpit or inside the limbs need to be spikeless, and maybe focus only in the frontside, and the spike is only around the chest or torso and frontside of the limbs, left the rest spikeless so at least you have place to grasp and fastening it safely, or you can keep it as is and left the back or side spikeless so you can fastening it from behind (likely need someone help) or the side.
and here another alternative if theres some monster with spiky skin.
from: pinterest
and regarding shield, since you mention they use gun, i recommend pavise type of shield, also add spike or blade to the frontside too, so the monster will have a hard time to get pass the shield preferably in bottle neck location or close tight terrain with low roof to prevent this monster from climbing the wall or jump over such as in front of the door, windows, or tunnel, otherwise try to position yourself in the high ground.
from:https://en.wikipedia.org/wiki/Pavise 987