How do you not forget to follow up with people?

I feel like I’m constantly losing track of follow-ups with potential clients. I talk to people over email or linkedin… and after a few days of multitasking at work, I just forget to get back to them. I’ve probably lost some opportunities because of that.

I tried using a spreadsheet and calendar reminders, but if I don’t check them regularly, things still slip when I get busy.

I read other posts about this problem and I know people usuallly suggest CRMs, but that feels like overkill for my situation.

Do you have some other ways to keep track of follow-ups so nothing slips?