If you have multiple size for your products, then using this app you can display all the sizes on the product page with a quantity field. Your customers can add quantities for multiple sizes and go to the cart page with a single click. This is available in the starter plan which is a free plan.
To do this, First you need to create your sizes as variants in your shopify store then apply multivariants. The app has 3 days of free trial period so you can explore other packages and features too and you will not be charged within the free trial time.
You can have other styles such as drop-down, swatch, grid-matrix style but those are on the other paid packages.