Complicated Laravel relationship to generate view - mysql

Question

I have Orders which contain any number of items stored in the items table (so a belongsToMany relationship between the two). The items are also categorized under itemtypes. When creating or editing an order I would like to load all items, categorized by itemtype, whether or not that order has any of the items. I was able to pull that up generically using the following:
$itemtypes = \App\Itemtype::with('items')
->orderBy('id','asc')
->get();
Then I loop through:
#foreach( $itemtypes as $itemtype )
{{$itemtype->name}}
#foreach( $itemtype->items as $item )
{{$item->name}}
#endforeach
#endforeach
This gives me something like:
NICU Items
- Baby Blanket
- Beaded Baby Cuddler
Miscellaneous Items
- Fitted Sheet
- Microfiber Towel
However, when I'm accessing a specific order which has records in item_order I want to display the saved quantities (stored in the pivot table). I know one way would be to add records for all items to item_order for every order created but that seems rather inefficient.
Item.php
public function orders() {
return $this->belongsToMany('App\Order', 'item_order', 'item_id', 'order_id') -> withPivot('id','quantity','createdby_user_id','weight','cost_billed', 'calc_by_weight', 'track_units');
}
Order.php
public function items() {
return $this -> belongsToMany('App\Item', 'item_order', 'order_id', 'item_id') -> withPivot('id','quantity','quantity_received','quantity_delivered','notes', 'createdby_user_id', 'weight', 'cost_billed', 'calc_by_weight', 'track_units');
}
UPDATE
I'm on the trail to a solution. I'm converting the collection to an array, loaded up with all items, modifying the array as needed, then using array_merge to replace the items that have quantities already in item_order.
This all works great - the only issue I'm having now is that when I load the order with it's items, items have an itemtype - a categorization and I'd like to group them by that. I'm not sure how to add a groupby to a relationship. If I figure it all out i'll post the full answer then.