Mouse.Hit targeting relative to character?

Good day! I'm currently working on an isometric camera game, where your character turns towards your mouse. The issue is, only method I found to do this was by using TargetFiltering to make the mouse react only to certain parts. So while you're on the level of ground, everything is okay, but going to a buildings second floor, character turning becomes a huge issue like this: https://i.gyazo.com/abd34ff724dfd1ea915519893bff3fc0.mp4

I'd need the mouse to find X and Z axels relative to Y axel of characters root part. Any ideas how to do this? Here's how I made it work so far:

local player = game.Players.LocalPlayer
local character = player.Character
local gyro = nil
local mouse = player:GetMouse()
mouse.TargetFilter = game.Workspace.Environment
local runService = game:GetService('RunService')
 
local function onCharacterAdded(character)
	local torso = character:WaitForChild('HumanoidRootPart')
	gyro = Instance.new('BodyGyro', torso)
	gyro.P = 500000
	gyro.MaxTorque = Vector3.new(0, 500, 0)
 
	local humanoid = character:WaitForChild('Humanoid')
	humanoid:SetStateEnabled(Enum.HumanoidStateType.Jumping, true)
	humanoid:SetStateEnabled(Enum.HumanoidStateType.Climbing, true)
	humanoid.AutoRotate = false
end

local function isnan(x) return x ~= x end
 
local function onRenderStep()
	if gyro then
		--local mouseHit = mouse.Hit.p
		local mouseHit = Vector3.new(mouse.Hit.x,character.HumanoidRootPart.Position.Y,mouse.Hit.z)
		print(mouseHit)
		if not (isnan(mouseHit.X) or isnan(character.HumanoidRootPart.Position.Y) or isnan(mouseHit.Z)) then
			gyro.CFrame = CFrame.new(player.Character.HumanoidRootPart.Position, mouseHit)
		end
	end
end
 
while not player.Character do wait() end
onCharacterAdded(player.Character)
player.CharacterAdded:connect(onCharacterAdded)
 
runService:BindToRenderStep('TrackMouse', Enum.RenderPriority.Input.Value, onRenderStep)

Thanks for reading!

I'm guessing that you're having trouble with making sure the character doesn't go ballistic when the mouse points at an object higher than the player's current Y position. If so,

What if instead of calculating the Y value at all, you just use the player's HumanoidRootPart's Y position, and the mouse's X and Z Hit Positions?