Well, Memoria Press is an advanced enough of a box so might be worth looking into.
I have had advanced learners here, too. My husband and I took the approach that just because they CAN doesn’t mean they SHOULD. Gifted kids (and it sounds like that is what you have) are asychronistic in their development. They need to be able to fly but slow down, too. We tried to remember that they were still just young. Don’t push. You have LOTS of time.
For the 3 yr old, my daughter LOVED Rod and Staff ABC and CLE Kinder II wkbks at that age. She also liked the EPS Books (now School Speciality) Get Ready, Get Set, Go For the Code books too, but I was ready to claw my eyes out! www.starfall.com is also a wonderful free resource.
R&S math Grade 1 is gentle enough for early learners, too. We really like BJU Math using the distance learning videos, too. Worth every penny. (This after more than 20 math programs. My oldest had math learning issues.) Just because a child can work the problems does not mean they grasp the why behind it. You want a good, solid foundation here or it will come back and bite you later. Once again, don’t push, you have lots of time.
Other resources we loved was Five in a Row (minus the reading 5 times). You can make loads of fun things from that or create your own. I would not agree it is complete at all, though, like the FIAR folks would have you believe. It doesn’t build in skills at all. Or simply pick your own favorite picture book and make your own activities. Another similar resource is Memoria Press’s Enrichment guides.You can add LOTS of hands-on things there- clay, blocks, etc…
All you need for handwriting is UNLINED paper and a wall chart. Use a highlighter to form the UPPERCASE letters first, then the child traces. Mine all learned this way and by practicing on their own. If you must have a wkbk, Handwriting Without Tears (minus all the “stuff” and TMs) is excellent. My other absolute favorite resource for handwriting/phonics is a free tracing page from a UK site called Promenthean Trust. I used the first sheet over and over. The kids learned letter sounds, letter names, trace the sound/letter you hear in ___ word, etc. all from that one page. It is gold and free! I probably have a corner of the rainforest gone with the amount of copies I have made of that page over the years! Do yourself a favor: print and laminate it. Use Extra Fine wipeable pens.
Hope this helps you as you begin your journey.