I had searched the solution and there was a tool named Kissflow that could help me but it was costly and for bigger team. That's why I decided to build a minimalist tool myself and I chosed Apps Script, a free script from Google to build a Google Forms addon. (Google Forms is simple & easy-to-use and I always have entrepreneurial mindset so I planned to upload to Gsuite Marketplace to have external users too)
Then, Firebase is for database due to its realtime feature, low cost, and generous free quota. Also, I used Google Cloud Functions to handle small tasks (backup, utilities,...) and things that Apps Script can't do.
The final result is PerformFlow, an add-on that can automate approval workflow via Google Forms. It was uploaded to Gsuite Marketplace and till now, it has some users. Thanks to the good response from users, I updated a new feature to generate & send PDF based on the feedbacks.
It's just a simple tool that utilizes Google Forms so I'd love to have your comment & ask me if there is any question!