If you take control over your keymap and break out of the idea that the keycaps have to say what the key actually does, the problem is rarely insufficient keys on the keyboard to do what you want, even before you start mucking around with layers or other fancy things. A key that you want to have at hand, but only occasionally, is fine on a SHIFT-CTRL or CTRL-ALT or CTL-Win setup and very few things are default bound to such shortcuts in general.
If it's only a couple of such keys, it is generally not too difficult to use someone else's keyboard if you need to; slightly annoying but you will recover how to do whatever it is you're doing right now reasonably quickly.
I recently switched to this 64-key keyboard: https://mistelkeyboard.com/products/0a26d32ac1e3b1d2af2896e0... I've got a setup where I put one half on each armrest. After a brief adjustment, it's fine, I've got everything I need at hand, and I use the keyboard like crazy; I have not obsessed over setting up a no-mouse setup, but I can hit the mouse single digit numbers of times per hour pretty easily. There's plenty of keys.
Indeed - I recommend a split keyboard with two split spacebars on both sides. The Ergodox or it's FOSS equivalents are really nice once you program in some useful things and there are many very good keymaps for plug-and-play.
I picked up the (back, del) (enter space) thumbs layout from Kinesis, that feature alone has saved me years of strain, id wager. The shape took a bit of time to get used to but I was back at my average wpm speeds in a couple of weeks. Not as much of a learning curve as Ergodox with its layers but the curve and ortholinear layout take a bit of adapting to, though that's true of the Ergodox too.
I kind of wish split keyboards were standard, instead of the default mode being all squeezed into the same 38cm wide form factor. The MS Natural keyboard was a step in that direction, split keyboard with a JUMBO space bar, but I wouldn't nominate it for the new standard..
While the kinesis doesn't have layers like Ergodox, it does have macros and you can remap keys via the hardware of the keyboard itself. I've been using an Ergodox for a few years now and got used to the layers but found the switches needed replacing a lot sooner (maybe I should have gone with a different set) and found the firmware update process for remapping to be annoying and tedious (even though they've gotten it down to about as few steps as is practical). Ergodox is more powerful in the abstract, though.
If it's only a couple of such keys, it is generally not too difficult to use someone else's keyboard if you need to; slightly annoying but you will recover how to do whatever it is you're doing right now reasonably quickly.
I recently switched to this 64-key keyboard: https://mistelkeyboard.com/products/0a26d32ac1e3b1d2af2896e0... I've got a setup where I put one half on each armrest. After a brief adjustment, it's fine, I've got everything I need at hand, and I use the keyboard like crazy; I have not obsessed over setting up a no-mouse setup, but I can hit the mouse single digit numbers of times per hour pretty easily. There's plenty of keys.