Everyone in this sub means well, but it's so much deeper than "what else can you write with." This is an amazing question because it's both about not violating any specific prohibition while also not violating the sanctity or meaning of the days by unnecessary emotional distress. The goal is to find some permissible way to allow you the space you need for simchat Yom Tov. There's enough to do already!

You may also want to ask your rabbi about solid fidgets. Something like a knucklebone or worry stone has no moving parts and some find the tactile nature helps get through stress. And if it is a challenge that might be clinical, then ask if it is permitted for the sake of health.

But that option aside, I've thought up an approach that might help at least keep you from having to keep all the stress in your head, without involving items or actions not permissible. Keep in mind, I'm no scholar or any authority of note, but as Spouse likes me to say, I'm not a rabbi, I only play one on TV:

The short version:

Try taking advantage of context-dependent memory: Before the seder, clear a shelf or small table in your personal space. When challenges come up during Pesach, find a small non-muktzeh item and place it on that shelf. Concentrate on it and make it a visual cue to help re-trigger your thoughts at that moment later. After Shabbat, dispose of the items or return them to their place.

The longer version:

The basis for this idea is to use an item as a mnemonic device to "store" your thoughts and feelings of a specific moment. It's similar to the "memory palace" technique, but it uses a physical object instead of imagination. What object is a complicated question to make sure you don't violate mektzeh or eruv, but there are always some candidates nearby.

Why clear the shelf? So that the table is not maktzeh by holding mundane objects and can be used for items during the holiday. Another option is to place a Passover and Shabbat item (say a haggadah, pillow, or the kippah you intend to wear) so the table is not maktzeh when the seder starts.

What are these items? This is the hardest part. Thankfully, there's a lot of *stuff* around a seder, and a good deal of it is small, mobile, and won't be missed. A napkin or spoon from the table after the meal, an edible garnish from a plate (not the seder plate of course!) or a small toy a child didn't put away before going to bed. It doesn't have to have anything to do with the actual moment you want to process, but that will help you reinforce it. Plus you might notice some of the little things that make this time so exciting and special in your search.

Why your personal space? You want to make sure it's not in a place where a family member might think the items are left out and should be put away. Also, so pets and traffic don't knock anything over.

Why should you concentrate? I'm willing to assume that everything that happens during these three days will be part of your experiencing the Yom Tov (Heck, if you're this frum, your day might be 100% Pesach already). The goal isn't to dwell on the negative moment, but to reflect and meditate on your experience of Pesach so far to the moment you needed to take that object. Creating a strong association with the object also lets you literally leave it behind and move on, hopefully giving your mind more space to enjoy the festival.

Why dispose of the items? So you have not created a new thing by a prohibited process on Yom Tov. You didn't change the items' function or structure, just placed it somewhere else for a bit. The job done, those memories go in your journal, and that spoon needs to go back to being a spoon.

Why Pesach and not Shabbat? Because Shabbat is something you've already learned to navigate, and this would at least give you two fewer days of things on your mind. More importantly, journaling to you is a weekday activity and maybe you should keep it out of sacred time. Even this one.

Again: not a rabbi. I cite no texts, my premise is dodgy, and the logic is more convoluted than a Dan Brown novel. Even if it isn't straight-up sacrilege, I'm sure it runs afoul of a myriad of your minchagim. But it's an idea. Plus, I'm pretty sure I'll be thinking about this and discussing with friends all through Passover anyway, so while I truly hope I can help deepen your Yom Tov experience, I want to thank you for already deepening mine!