As you have already noticed that there are two types of transaction interfaces one is UI and another is non-UI. If you want more control over your transaction like you want to control your transaction fee, using non-UI will be better choice.
On the other hand if you do not want to bother yourself with this you can choose UI interface and create a payment sheet UI. The payment sheet UI will handle the transaction fee for you.
You can find more about implementation of the payment sheet UI interface here and see the ERC721 section to select the right choice for your application.
But if you want to develop a Dapp and want to transact form a website, Samsung Blockchain Platform SDK provides a webview named Cucumber webview. Cucumber webview also provides payment sheet UI.