Shopify Customization

Hello, I have a Shopify website I want to do some customization on it. My Shopify website is a boutique online store I need to add a custom size option for customers. I have mentioned the demo link here you can visit and check the custom size option if you do that for me.

My Website: www.khodgi.com

Demo website: https://jazmin.pk/collections/fusion-of-deluxe/products/cherry-rose-a?variant=40020857684012