Ergonomics was a large factor in building my own ErgoDox, my shoulders were killing me due to the keyboard being too short to be supported by the rests on my chair. Choosing to build your own keyboard is it's own little rabbit hole to go down, but it's worth it and you have a truly personalised device at the end. Some soldering and research is required but places such as r/mechanicalkeyboards and geekhack exist along with many many tutorials.
As far as curved keywell that comes down to your choice of key profile. I'm using XDA which a flat profile, while a SA profile has a decent curve to it. The choice of board does come into play but most kits are flat as to avoid 3d printing and whatnot[1]. For the feel of the key itself there are a ton [2] of options, from extremely smooth and light linear switches to heavy clacking tactile switches,
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most being compatible so mixing and matching is possible. PCBs come in all sorts such as tiny 70% sizes, split, stenographic and some freakazoid monsters [3]. Even FOSS firmwares such as QMK are common and hackable! There are are too many options to enumerate!
I just wanted a split keyboard that was small, light on my fingers and wouldn't wake the girlfriend up. I took some time and built a ErgoDox with Gateron clears, XDA blank keycaps and a programming focused layout. For less then 150CAD, it was worth it for it being entirely my own.
[1] https://github.com/adereth/dactyl-keyboard
[2] https://deskthority.net/wiki/Category:List_of_all_keyboard_s...
[3] https://keeb.io/products/bfo-9000-keyboard-customizable-full...