I would like to recommend theMultiVariants ‑ Bulk Order appwhich can provide the functionality you're after. This app allows your customers to mix variants as well as multiple amounts of one variant to a certain limit restriction you put in place. The ordering process is made simple for your customers which is also an important aspect to factor in so I would highly recommend adding this app to your store. The app offers a 3-day free trial so you can test out it's features and ensure it is appropriate for your online store before committing to a paid plan.
If an app is not a suitable option for your online store, you can take a look at ourShopify Experts Marketplaceand hire a developer who may be able to install this onto your website. You'll be able to filter your search according to your own budget, location, language and rating!
Nia | Social Care @ Shopify - Was my reply helpful? Click Like to let me know! - Was your question answered? Mark it as an Accepted Solution - To learn more visit the Shopify Help Center or the Shopify Blog