DISCLAIMER: I HAVE NO IDEA IF SOMEONE ELSE MADE A SIMILAR GUIDE OR EXACT GUIDE AS THIS.

This is a little guide I made to tell you how to completely attach the thirdpersonshoulder camera to the survivor's head. This means the camera will completely follow the survivor's head. From crouching to jumping to getting punched, pounced, staggered, et cetera. Best of all NO MODS REQUIRED! This is something you can do right from the developer console. In case you ask "Does this work in multiplayer?" IDK. I think it would only work in co-op since you can't go into thirdperson on versus. I haven't tested, but I don't see why not. I do also believe sv_cheats has to be enabled but I'm not sure because I haven't tried.

PLEASE NOTE THAT MY FOV WAS SET TO THE DEFAULT VALUE (90) WHILE SETTING THIS UP. THIS IS RECOMMENDED. ALSO, THESE SETTINGS ARE SET FOR THE ORIGNAL L4D 1 & 2 MODELS. CUSTOM MODELS HAVE DIFFERENT SETTINGS BECAUSE OF THE DIFFERENT BONES IN PLACE.

!!IMPORTANT COMMAND!! YOU HAVE TO SET THESE EACH TIME YOUR A SPECIFIC CHARACTER. (this command sets the thirdperson camera to the head bone of the model, in other words, attaches)
For when your Rochelle: cl_camera_follow_bone_index 16
For when your Coach: cl_camera_follow_bone_index 17
For when you Nick: cl_camera_follow_bone_index 14
For when your Ellis: cl_camera_follow_bone_index 14
For when your Zoey: cl_camera_follow_bone_index 14
For when yours Louis: cl_camera_follow_bone_index 14
For when your Francis: cl_camera_follow_bone_index 14
For when your Bill: cl_camera_follow_bone_index 14

AFTER THE IMPORTANT COMMANDS ARE ENTERED, ENTER THESE COMMANDS
cam_idealdist 0 cam_ideallag 0 cam_idealpitch 0 cam_idealyaw 0
c_thirdpersonshoulderaimdist 1000 c_thirdpersonshoulderoffset 0

You should be all set now. Like I said, most, if not all, custom models have different bones in place and so the head bones are set at different values, from the ones I've tested. So you'll have to play around with the "cl_camera_follow_bone_index" command for when your playing as your custom model. For example the head bone on the Arcane Jinx model for Louis is bone_index 55 and the Meow Skulls model for Zoey is bone_index 16.