How to save size to cart in django-oscar?

Question

Django

Hello, I'm trying to customize saving a product to the cart.
First I changed the model

from oscar.apps.basket.abstract_models import AbstractLine

class Line(AbstractLine):
    size = models.IntegerField(default=0)

After changing shape

<form id="add_to_basket_form" action="{% url 'basket:add' pk=product.pk  %}" method="post" class="add-to-basket">
        {% csrf_token %}
        {% include "partials/form_fields.html" with form=basket_form %}
        {{basket_form.size}}
        <button type="submit" class="btn btn-lg btn-primary btn-add-to-basket" value="{% trans "Add to basket" %}" data-loading-text="{% trans 'Adding...' %}">{% trans "Add to basket" %}</button>
</form>

I'm trying to add the size field as above in the html code, but I can't find it.
Tried to change shape

from oscar.apps.basket.forms import AddToBasketForm, 
class AddToBasketForm(AddToBasketForm):
    def __init__(self, *args, **kwargs):
        return super().__init__(*args, **kwargs)

    size = forms.CharField()
    
    class Meta:
        fields = '__all__'

Can't find it either, can you tell me what to do next? It turns out that I want to display the size field in the form and save it to the basket of the product.