How do i add multiple enemies to my unity wave system?

Question

I have a wave script for my game and it works fine, however after a while I have realised it gets quite dull fighting against the same enemies over and over again, so I was wondering if I could make a list of some sort to store all enemies that will be in each wave.

Here is my script;

SpawnManager.cs

  using System.Collections;
using UnityEngine;

[System.Serializable]
public class Wave
{
    public int EnemiesPerWave;
    public GameObject Enemy;
}

public class SpawnManager : MonoBehaviour
{
    public Wave[] Waves; // class to hold information per wave
    public Transform[] SpawnPoints;
    public float TimeBetweenEnemies = 2f;
    public GameObject HelpText;
    public GameObject Shop;
    public GameObject shopfx;
    public Transform ShopL;

    bool shopactive = false;

    private int _totalEnemiesInCurrentWave;
    private int _enemiesInWaveLeft;
    private int _spawnedEnemies;

    private int _currentWave;
    private int _totalWaves;

    void Start ()
    {
        _currentWave = -1; // avoid off by 1
        _totalWaves = Waves.Length - 1; // adjust, because we're using 0 index

        StartNextWave();
    }

    void Update() 
{
    if (_enemiesInWaveLeft <= 0 && Input.GetKeyDown(KeyCode.R))
    {
        StartNextWave();
    }
}

    void StartNextWave()
    {
        _currentWave++;

        // win
        if (_currentWave > _totalWaves)
        {
            return;
        }

        _totalEnemiesInCurrentWave = Waves[_currentWave].EnemiesPerWave;
        _enemiesInWaveLeft = 0;
        _spawnedEnemies = 0;

        StartCoroutine(SpawnEnemies());
    }

    // Coroutine to spawn all of our enemies
    IEnumerator SpawnEnemies()
    {
        GameObject enemy = Waves[_currentWave].Enemy;
        while (_spawnedEnemies < _totalEnemiesInCurrentWave)
        {
            _spawnedEnemies++;
            _enemiesInWaveLeft++;

            int spawnPointIndex = Random.Range(0, SpawnPoints.Length);

            // Create an instance of the enemy prefab at the randomly selected spawn point's 
            // position and rotation.
            Instantiate(enemy, SpawnPoints[spawnPointIndex].position, 
                             SpawnPoints[spawnPointIndex].rotation);
            yield return new WaitForSeconds(TimeBetweenEnemies);
        }
        yield return null;
    }

// called by an enemy when they're defeated
public void EnemyDefeated()
{
    _enemiesInWaveLeft--;
    
    // We start the next wave once we have spawned and defeated them all
    if (_enemiesInWaveLeft == 0 && _spawnedEnemies == _totalEnemiesInCurrentWave)
    {
        HelpText.SetActive(true);

        Invoke("SetFalse",5.0f);

        Shop.SetActive(true);

        Invoke("LateUpdate",1f);
        Instantiate(shopfx, new Vector3(ShopL.transform.position.x, ShopL.transform.position.y, ShopL.transform.position.z), Quaternion.identity);
        shopactive = true;
    }

    

}

void SetFalse()

    {
        HelpText.SetActive(false);
    }

void LateUpdate()
{
    if(Input.GetKeyDown(KeyCode.R) && shopactive == true)
    {
        Shop.SetActive(false);
        Instantiate(shopfx, new Vector3(Shop.transform.position.x, Shop.transform.position.y, Shop.transform.position.z), Quaternion.identity);
        shopactive = false;
    }
    
}

}