Can we keep trademarking costs down if we use variations of our main brand?

We would like to protect our brand as a registered trademark. We have been using our company name as the brand for our main product, so we were wondering if in the beginning it would be enough to register only that as a trademark and keep costs down.

In case we develop a spin-off service the marketing of which would be independent of the main product, we would probably use a different brand though. We were wondering if the protection we would have for the main brand could be somehow expanded onto other products without us having to register for each brand individually. As an example, let's say our main product and our company was called "Rocketize" and we had a trademark registered. Could we for instance brand a product with "Rocketize Pro", "Rocketize Enterprise", "New Rocketize", "Rocketizer" and so on and still have these brands protected under the original registration?