• at the maximalist end of things – Ergodox form factor – ZSA Moonlander or Ergodox EZ
• middle road – Promenade (formerly Boardwalk) – fits into 60% case, uses Ergo keycap sets
• minimalist route – lose out on center columns – Lumberjack – fits into 60% case
• micro path – Lesovoz – fits into Minivan case

If you need some inspiration on existing boards: https://golem.hu/board/ --> set the filter on "ortholinear" for "matrix style" boards.

First you need to find a board, then we can help you to build it.

(You COULD build a board from scratch, but if you have not built a board yet, or have no background in mech. / electr. engineering, this me a bit too much at first.)

I used to have a TypeMatrix around 15 years ago and really enjoyed it, but the rubber domes wore out on me. Happy to hear that yours survived that long!

There is a commercial product with big keys in the middle - the Truly Ergonomic, which I got afterwards. The new version has optic switches, and you can reprogram the middle keys. I also had the Cleave and have to say, those switches are damn smooth, but I prefer the layout I set up on my Moonlander.

Lazy path: just buy an remap a Kinesis 360 Pro. It's perfectly fine to just go with some off-the-shelf perfection and procrastinate all the time you've saved.

Going completely in the other direction from the "lazy" side, you could recreate the layout in the KLE keyboard layout editor, have a top and bottom plate cut at xometry or another vendor, either handwire or design a PCB and have it made by JLCPCB or another vendor, and use blank keycaps or see about making/procuring custom legends. 5u spacebars are a rarity (and 5u x 1.25u are basically not a thing), but if you're willing to split it into a 2.75u and 2.25u, then you could use the shifts from any random 104-key XDA set. Don't quote me on this, but glancing at the 2030 there, I think a non-sculpted blank 104 set would work fine if you did that. 4@2u, 1@1.75u, 2@1.5u, and 1@1.25u once you bump the f-row up to being proper 1u keys. If you wanted to go half measures, you could get a cheap dye-sub XDA set as well as some blanks, and have your most of your 1u keys be accurate and maybe even a couple of the larger ones.