That's a brilliant idea! I've been using a notes app for my self care 'to do' list, but a physical calendar I can see and interact with would be so satisfying.
I also love the idea of scheduling playdates and dates nights as reminders of your pre-motherhood life - it's so easy to forget yourself amidst the all encompassing nature of parenting!
My personal approach has been to set up weekly 'me time' sessions, where I block out a few hours each week just for myself. Sometimes it's an evening yoga class, sometimes it's catching up with friends for drinks or coffee, and sometimes it's an afternoon reading a book in peace - the key is that it's protected time, no distractions or guilt!
I've found keeping it as a weekly occurrence helps me keep on top of my mental health too, rather than letting it become something I only do occasionally. Also, knowing I have that time coming up keeps me focused and motivated during the busy weeks!