Karlie here from the Shopify Support Team! If you have a product with more than 100 variants, then you could use an app to provide your products with more options. There are quite a few apps in the Shopify App Store that would help you achieve the functionality you're looking for. Specifically I would recommend you to check out the apps; Infinite Product Options, Best Custom Products Options, and Dynamic Product Options. These three apps have higher ratings in the Shopify App Store and merchants seem to have a lot of success using them.
I hope this has answered your question. If not, or if you have any further questions please let me know. I will be happy to help!