What's the best app for customizing product variants?

Hi

You should be able to set this up with the existing option set up:

https://help.shopify.com/en/manual/products/variants/add-variants

If you need more than 3 options than consider using an options app that lets you use more and doesn’t limit variation count to 100:

https://apps.shopify.com/search?q=options

Main limitations of options apps are there is no inventory control. If you need this check out Bundleup as you can style your product as normal and with standard variations but in the backend select what components they contain so inventory is correct.

https://help.channelup.com.au/hc/en-us/articles/900004620086

Regards

Sam