How can I make the FPS arms stay with the camera?

So, I'm making a gun for an FPS. I already have the script for showing the FPS arms, and animations, etc. I'm just having trouble with having the arms follow the camera. Basically, I want the torso to move to the Y point of the camera but I don't want the legs to move with the torso. I have this code here:

mouse.Move:connect(function()
		mouse.TargetFilter = game.Workspace
   		torso.CFrame = CFrame.new(torso.Position, Vector3.new(mouse.Hit.p.X, 			  mouse.Hit.p.Y, mouse.Hit.p.Z))
end)

It works decently, but if your arms touch the ground then it like flings you and makes you fall. Also, the entire body moves; like, the legs also float with the torso. I want the legs to stay flat on the ground, and only have the torso move up and down on the Y axis according to the Y of the mouse. I was thinking of making the head move with the Y and welding the arms to the head, but I'm not sure to do that. Could anyone help me please? Thanks!

for FPS I prefer to use R6 real arms this is my local script:

plr = game.Players.LocalPlayer;
repeat wait() until plr.Character
char = plr.Character
m = plr:GetMouse()
game["Run Service"].RenderStepped:connect(function()
local c = game.Workspace.CurrentCamera

char.HumanoidRootPart["RootJoint"].C0 = CFrame.new(0,0,0) * CFrame.Angles(-math.asin((m.Origin.p - m.Hit.p).unit.y) + 1.55,3.15,0)

	char.Humanoid.CameraOffset = (char.HumanoidRootPart.CFrame+Vector3.new(0,0,0)):pointToObjectSpace(char.Head.CFrame.p + Vector3.new(0,-1.46,0))

end)