Free Movement (Space/Underwater) With First Person Controller

Hey guys, I have spent the past few weeks stumped trying every scrip and answer trying to get this to work. I am trying to get the first person controller to be able to move up and down along with the default sideways/forwards/backwards. Can anyone help me out? Thanks.

You would have a first create a new controller based off of rigidbodies, as the regular one is weak for anything other than what it was made for (plus, coding your own is better always). As said, you should have a bool for if the player is underwater. If he is, his jump (using AddForce) with happen as long as your underwater. I’ll help you as making your own controller feel nice takes a bit of testing.
(this is based off my own controller, unlike mine though this doesn’t have a separate script for just taking in input)

using UnityEngine;
using System.Collections;

public class PlayerController : MonoBehaviour {

	private bool _Jump;
	private bool _Crouch;
	private bool Running = false;
	private float Speed = 0;

	[HideInInspector]
	public bool losingStamina = false;
	[HideInInspector]
	public bool canJump = true;
	[HideInInspector]
	public bool isMoving = true;
	[HideInInspector]
	public bool isGrounded = true;
	[HideInInspector]
	public bool isUnderWater = true;

	public float walkSpeed = 10;
	public float runSpeed = 15;
	public float AirModifier = 1.5f;
	public float fakeFriction = 0.86f;
	public float jumpForce = 40;
	public float isGroundCheck = 1;

	void Update () {
		//Speed Modifier
		if (Running == true && isMoving && isGrounded) {
			Speed = runSpeed;
		} else if (Running && isMoving && isGrounded) {
			Speed = walkSpeed;
		} else{
			Speed = walkSpeed/AirModifier;
		}

		isGrounded = Physics.Raycast(transform.position, -Vector3.up, isGroundCheck);
		Running = Input.GetKey(KeyCode.leftShift);
		_Jump = Input.GetKeyDown(KeyCode.Space);
		float h = Input.GetAxis("Horizontal");
		float v = Input.GetAxis("Vertical");

		if(h >= 0.1 || h <= -0.1 || v >= 0.1 || v <= -0.1 || _Jump){
			isMoving = true;
		}else{
			isMoving = false;
		}

		//Limit Speed
		if(rigidbody.velocity.magnitude > Speed){
			rigidbody.velocity = rigidbody.velocity.normalized * Speed;
		}

		//Movement
		this.rigidbody.velocity = new Vector3 (this.rigidbody.velocity.x * fakeFriction, this.rigidbody.velocity.y, this.rigidbody.velocity.z * fakeFriction);
		Vector3 MovementForce = new Vector3 (move.x, 0, move.z);
		MovementForce.Normalize ();
		Vector3 MoveForce = transform.TransformDirection (MovementForce);

		if (Moving) {
			rigidbody.AddForce (MoveForce * Speed);
		}

		if (isGrounded && canJump && _Jump || isUnderWater) {
			rigidbody.AddForce(transform.up * jumpForce, ForceMode.Impulse);
		}
	}
}