How to use a ManyToMany field in django with a through model, displaying it and saving it?

Question

I am doing a basic system in Django for a Spa that requires me to have an inventory, massages that use different quantities of product in the inventory, and then a service which will be a combination of multiple massages. So the user of the spa, which is the staff, will be able to create a service, select which massages make that service, and that will instantly trigger the subtraction of that product from the inventory. I used a many to many relation to relate the massages and the items, with a through model to save the amount used as well. My question is, what would be the best way to display this in a form so the staff can add new massages in a way where they can choose many items and their respective quantity that the massage will use? And how can i save all of this afterwards into the DB? I'm using PostgreSQL. This is how my models look right now:

class Producto(models.Model):
    
    nombre = models.CharField(max_length=200, blank=False)
    línea = models.CharField(max_length=200, blank=False)

    proveedor = models.CharField(max_length=200, blank=False)
    costo_mxn =  models.DecimalField(blank=False, max_digits=10, decimal_places=2)

    unidad_de_medición_choices = [
        ("g", "g"),
        ("mL", "mL"),
        ("oz", "oz"),
    ]
    
    unidad_de_medición = models.CharField(max_length=20, choices=unidad_de_medición_choices,null=True, blank=True)
    cantidad_actual = models.DecimalField(blank=False, max_digits=10, decimal_places=2)
    cantidad_inicial = models.DecimalField(blank=False, max_digits=10, decimal_places=2)
    cantidad_alerta = models.DecimalField(blank=False, max_digits=10, decimal_places=2)

    fecha_de_registro = models.DateField(blank=True,null=True,default= datetime.today)
    def __str__(self):
            return self.nombre
class Masaje(models.Model):
    nombre = models.CharField(max_length=200, blank=False)
    productos = models.ManyToManyField(Producto, through='CantidadProducto',blank=True)
    costo = models.DecimalField(blank=False, max_digits=10, decimal_places=2)
    duracion = models.DurationField()
    descripcion = models.TextField(
        max_length=500, blank=True, null=True
    )

class CantidadProducto(models.Model):
    masaje = models.ForeignKey(Masaje,on_delete=models.CASCADE)
    producto = models.ForeignKey(Producto,on_delete=models.CASCADE)
    cantidad_usada = models.DecimalField(blank=False, max_digits=10, decimal_places=2)

Now I've been using simple forms to display other parts of the system that I've done that aren't as complex, for example the masseuse, like this:

class MasajistaForm(ModelForm):
    class Meta:
        model = Masajista
        fields = (
            'nombre',
            'telefono_celular',
            'fecha_de_nacimiento',
        )
        widgets = {
            'nombre': forms.TextInput(attrs={'class':''}),
            'telefono_celular': forms.TextInput(attrs={'class':''}),
            'fecha_de_nacimiento': forms.SelectDateWidget(years=range(1900, 2023),months = MONTHS,attrs={'class':''},empty_label=("Año", "Mes", "Dia"))
  
        }

With a result like this

Now, i know it doesn't look great but that's not the problem right now, I would like it so the staff can see a form like that where you could maybe hit a plus button or something like that where a new select box would appear with a selection of the already registered items, and an input box that could be filled by hand and then saved. What would be the way to go here?