For planning our days, I use a to-do app called TickTick. I hunted high and low for the just-right to-do app for our homeschool life, and this is it. It's calendar-based, and lets you set up recurring items.
For instance, every day we do math, so I set that up once and get to check it off each day without having to uncheck or re-add it. There are other subjects, like handwriting, that don't need to happen every day, but I don't want us locked into a rigid ON TUESDAYS AND THURSDAYS WE WRITE FANCY life. TickTick makes it easy to slap it in there on Tuesdays & Thursdays, and then just pull it or push it to the day we'll actually get to it. It doesn't get dropped, but it's not nagging at me all the time that I really need to fit it in somewhere. Frees my brain up for the fun stuff.
Speaking of fun stuff, much of what we do in a day is following what makes sense in the moment, so I have a sort of loose list of possibilities each day, and anything I don't get to I can easily move to a day later in the week.
The interface is SUPER slick, it's a breeze to move things around. It's easy to shuffle the order of things in a day, and it's easy to look over a coming week and redistribute overloaded days' items onto lighter days. Because items are specifically plotted to days, I find it doesn't turn into the growing-avalanche-threat-of-guilt of accumulated undone tasks I've experienced with other to-do apps.
TickTick also supports to-do lists within a to-do list item. Our science curriculum uses the Socratic method heavily, and this lets me map out the path of understanding I'll be leading her down in a particular lesson so I don't need to lug the teacher's manual with me.
I find that for us, homeschooling works best when I find a balance of regular rhythms she can count on, coupled with wild flexibility to follow the natural highs & lows of passion or energy level. Offloading keeping track of it all to my phone frees us up to do what's best in the moment without my brain frying.