If you want lots of differently styled templates, template management and editing/styling capabilites in word or excel (ie. you can just ask your customer/employer/.. to make an example document), I can really recommend Carbone [0]. I've been a happy customer for a few years now. Extra advantage is also that it also offers you excel outout generation as well, which is also often a requirement in applications. They have a SaaS offering as well if you'd like. They are open source though, so you can easily run a docker container!

[0]: https://carbone.io/