Probably not a great suggestion these days. Back when I first got carpal tunnel / RSI (1995), I was using an IBM model M - which I loved the feel of. I had a dream of cutting a keyboard in two and hanging two halves off my chair so I could drop my arms to my sides and type that way.

Anyway, after trying a couple of things, Microsoft Natural (the original with backtilt) saved my programming career. I still have "weak" wrists/fingers/forearms, but it's rarely painful enough for me to have to stop working. Adding in some stretches generally makes it so I can survive.

I can type on a normal keyboard for maybe 15 minutes and maybe an hour on a laptop before I just can't anymore. I can generally go most of the day on my Microsoft Natural. Retraining from a regular keyboard layout (took typing in high school - yes, I'm ancient) wasn't hard at all - it's basically the same.

Sure, it's technically not a "split" keyboard - it's still one thing. These days, I buy used examples off ebay, usually 3 at a time, and on some, the typing action is horrible - but I still have a couple of examples that are usable. And I had to find the right ps2->usb adapters for my work setup. If I ever totally run out, my professional coding days are probably done.