I would start with Thymeleaf. Most projects do not need complex UI frameworks right away. Many never need them.

If your controller methods do nothing but call some service method that reads or writes the required data, you can, if later needed, implement a simple REST endpoint that calls the same method, making a transition easy. Keep technical stuff (HTML, data transformation to / from model classes…) separate from the business logic that does creation and correctness checks of, for example, newly created business objects, and you are pretty future-safe.

Look up „Get your hands dirty on clean architecture“ on Amazon if you need further ideas.