You’re overthinking things. I am an older player. I’m retired and have had endured two massive strokes. My brain doesn’t work the same as it used to. But I don’t have any issue with WoW buttons count. But I used to, so let me explain how I overcame it.
First, stop overanalyzing things. The stress alone will impede progress. Next, compartmentalize what you do have. Instead of lining things up on your bar, according to some supposed rotation, split things up into small, logical blocks. I have one strictly for damage (long case opener, dots, direct damage, aoe damage). I have another for buffs, another for debuffs, and yet another for special procs.
Remember, the rotation sites are based on optimal situations. Most of the time, these don’t exist. Get an add? You whole rotation just goes pfft. Instead, prioritize things for the way you fight and your chosen content. It is perfectly okay for a given situation not include some of things in the rotations listed on those sites.
I think they are doing the one-button thing tomorrow. I suggest you do not use it. Use the other alternative, where it simply highlights the next button. That way, you can see that as fight dynamics change, so too does your rotation.
Be adaptable, and not so focused of rigidity. That’s what’s causing a lot of your stress. Relax, organize, prioritize, and relax some more. Have fun with it.