Synchronizing with Public/Open Source source code

Usecase/Problem Scenario :
- I am using an opensource source project as a base for my project.
- I need to make my custom implementation/changes.
- But the open source project is still under active development.
- I need to merge the changes from public project to private project which is in another repo.

Solutions is:
1. Clone the public project in local.
git clone -o https://github.com/sample_project.git

2. cd into the your project, which you have clonned already.
cd my_project

3. add the base project as a remote reference to your repository
git remote add -f base_project C:\sample_project

4. Pull the changes.
git pull base_project master --allow-unrelated-histories

5. Resolve the conflicts & commit

Limitations:
- Need to perform the pull manually each time. Which is in another way is safe.

Above is the solution which I formulated based on the references I made. Please let me know is there any further limitations in this approach.
Welcome if there any better alternative of this use-case.