Set int to object from list?

Hey! I've been working with saving for a while now, and I've run into an issue. I know how to stop the issue, I just don't know how to code it.

I have upgrades in my game, and each upgrade should have it's own separate "isFirstUpgrade" int. I'll be saving these later, so I'm converting bools into ints that only use 0 and 1 (0 being true 1 being false). I don't know what I should do with this, any ideas? Here's the code

     public int UnlockLevel;
     public bool isUnlocked;
     public Button ShopItem;
     public Click click;
     public ItemManager itemManager;
     public ItemLevels itemLevels;
     public bool FirstUpgrade = true;
 
     // Use this for initialization
     void Start () {
         
     }
     
     // Update is called once per frame
     void Update () {
         if (isUnlocked)
         {
             if(click.tobys >= itemManager.cost)
             {
                 ShopItem.interactable = true;
             }
             else
             {
                 ShopItem.interactable = false;
             }
 
         } else {
             ShopItem.interactable = false;
         }
 
 
 
         if(UnlockLevel <= itemLevels.Level)
         {
             isUnlocked = true;
         } else
         {
             isUnlocked = false;
         }
     }
     public void OnClick()
     {
         if (FirstUpgrade)
         {
             itemLevels.AddLevel();
             FirstUpgrade = false;
             itemManager.PurchasedItem();
         } else
         {
             itemManager.PurchasedItem();
         }
     }

Just a note that this script goes into each upgrade object.