Keeping in touch you used to do in a rolodex. You could keep track of the details per contact on separate cards and make (very) short notes. However, this was of course always on your desk, so if you were on the road, you were out of luck. A quick search was not an option.
Fortunately, things are different today. Nowadays everyone has a smartphone in their pocket, which in itself actually contains an entire CRM system. Contacts, calendar, email, notes, you name it, and it's there.
However, after a while you discover that just saving contacts, emails and notes is not that convenient. If you use it a lot, you quickly lose the overview. All contacts are there, but who did you have to call again? And what was recently discussed with that new contact?
That is why a simple CRM system is really essential. We have been using it for some time now Airtable. This allows you to build your own CRM yourself. Very simple with just people and activities? Or would you rather be very extensive with links to send emails, track leads, etc.? That's all possible Airtable. And as you are used to, we love that you can get started with it for free. You only have to pay if you want more functions, but that is certainly not necessary.
A tip, start small. Start quickly. Use a simple CRM template and get started. You will soon find out whether you need more functions, or whether you are not using certain things.
Good luck!