You can add size attribute in clothing category -> custom field tab and then you will see the select option on clothing categories product.
In Category Custom Field:
- If you add in core fields it will show in the specification section on product detail page
- If you add in variant fields it will display as variant option on product detail page
I've added XS size in an attribute, you can use it now.
But I checked and wanted to tell you, only one attribute can be chosen in a product and additional size's you must create its variants then your redirection issue will resolve automatically.
Delivery info under variants has been removed from our upcoming version and will do it on your site also.
And regarding variants dropdown, this has been also redesigned and fixed will do it on your site also.
I've made some changes on variant as well as on delivery info section, please have a look.
We are releasing our next version very soon and yes upgrade version will affect few thing if we directly upgrade it, we actually have to compare files first.