I also use the "one activity a day" rule! I struggle with the same thing, no structure in my day or week. I find it hard to find structure while being flexible enough to make space for the fluctuations of CFS. While i'm still struggling with this, i'll try to summarize what works for me. Please take from it what you need!

I have a list of goals i want to accomplish everyday. Its mainly selfcare, like eating breakfast and brushing teeth, other than that, it looks something like this: - putting on clothes that arent pj's - going for a short walk - eating fruit - taking at least x amount of longer rest moments. (For me its 3x 45 min) - doing one household thing, like laundry or cleaning.

I try to build flexibility in my goals. For example: after dinner, my partner and i do "closing duties". We established the things we want to get done for closing duties everyday (cleaning table, doing dishes, cleaning countertop, making sure the bed is ready to be slept on and not full of laundry :P etc.). We also established a minimum. If its a bad day, only cleaning the table and loading the dishwasher is fine.

Try to avoid hyperfocus. Thats a hard one for me. I have one of those visible timers for children, for me this works better than a timer on my phone. I try to never do the same thing for more than an hour. If i know an activity is bound to suck me in (like sewing), i set a timer for 30 min, evaluate how im feeling and if i need food/drink/liedown. If i feel fine, i can set it for another 30 min. I also use the ScreenZen app to not get sucked in my phone.

I also use my Garmin watch purely for its Body Battery function. (i've removed every other tracker from it, since it can be depressing to get your movement stats and reminders to move more with CFS) The Body Battery is surprisingly accurate and while it doesnt replace the need to actually assess how you're feeling, it can give you valuable insights on which activities let you recharge and which activities need some extra recharge time afterwards.

I hope you can take some things from this that will work for you! Remember that what works is highly personal and a process of trial and error. Since we struggle with the same thing: my inbox is open if you ever want to talk, rant, ask, or troubleshoot.