Clothing size chart problem

Using Django Getting Started
1

Hello, I am making a dress sales website. Everything was going well until now, but now I’ve stopped.

The problem is as follows

I store my products in different tables in SQL, and the size and stocks in different tables. I have no information about how to take the size measurement during the ordering phase, I need help with this. I’m looking for an example or a way to go.

Product Model:

class Urunler(models.Model):
    urun_baslik = models.CharField(max_length=100, verbose_name="Ürün")
    urun_anakategori = models.ForeignKey(AnaKategori,on_delete=models.CASCADE,verbose_name="Ürün Anakategori")
    urun_seo = models.CharField(max_length=100, verbose_name="Ürün Seo")
    urun_fiyat = models.DecimalField(max_digits=6,decimal_places=2, verbose_name="Piyasadaki Fiyat")
    urun_satis_fiyati = models.DecimalField(max_digits=6, decimal_places=2,null=True, verbose_name="Bizdeki Satış Fiyatı")
    urun_aciklama = models.CharField(max_length=100, verbose_name="Ürün Açıklama")
    """urun_stok = models.IntegerField(verbose_name="Stok")"""
    urun_renk = models.CharField(max_length=50, blank=True, verbose_name="Renk")
    urun_aktif = models.BooleanField()
    urun_resim = models.ImageField(blank=True, null=True, upload_to="urunresim", verbose_name="Ürün Resim")
    
    class Meta:
        verbose_name = 'Ürünler'
        verbose_name_plural = 'Ürünler'
        
    def __str__(self):
        return self.urun_baslik

    def resim_goster(self):
        if self.urun_resim:
            return mark_safe('<img src="{}" width="100" height="100" />'.format(self.urun_resim.url))
        return ""


    def get_absolute_url(self):
        return reverse("home:urundetay", kwargs={"seo": self.urun_seo})

Size Chart:

class Beden(models.Model):
    urun = models.ForeignKey(Urunler, on_delete=models.CASCADE, related_name="Beden")

    beden_tur = models.CharField(max_length=5, verbose_name="Beden")

    beden_stok = models.IntegerField(verbose_name="Stok")

When the product is sold, I want to get the size measurement as well, that’s all.