Yes your approach is correct.
Permission Sets are usually used for that very reason i.e. to extend user's access without changing their profiles.
When to use Profiles
- If there are two completely different types of users (like sales users and service users) sharing the same profile and if you feel that one type of users might require additional permissions in future.
- If you want to provide that additional access to very large number of users
then you can clone the existing profile and add that additional permission in new profile and assign this cloned profile to the required users. Although this can be achieved using permission set as well, but it is always better to have seperate profiles for two completely different sets of users which may require different permissions in future.
When to use Permission Sets
Permission Sets are useful when you want to extend the access to users in addition to the permissions provided by their profiles.
If this additional permissions needs to be provided for very less number of users