I always found these to be useful. You probably already know about them though: https://www.amazon.com/Razer-Nostromo-PC-Gaming-Keypad/dp/B004AM5RB6
fully programmable with the included software.
Reminds me of the Nostromo game pad I used to use.
I've got a few suggestions that might be useful.
First is something along the lines of the Razer Nostromo PC Gaming Keypad (amazon link) It's a combo mouse keypad for one-handed use. 16 buttons
or
Or the Razer Tartarus v2 Gaming Keypad (amazon link) 32 programmable keys
That will at least give you a decent starting point to search for other possible models.
There is one other thing that you might want to think about in addition to one of those things - using programmable footpedal inputs to give you more key options by using your feet.
Finding one that fits your needs and doesn't cost a fortune can be hard. I wanted a set of pedals for flying helicopters in ArmA, but I decided to build my own instead for under $40. I used this thing called a Makey-Makey board, that's designed for kids that lets you turn just about anything into a keyboard/controller input device - regular old buttons/switches for a controller or even make a piano out of bananas, lol. You can have up to 16 programmable buttons, no soldering or complex electrical or programming skills needed.
The one I built has two separate ramps/stands made from the backplates of some old computers, one for each foot, with two big 2 inch diameter buttons like you would find on an old arcade game. I use them for keybinds that I might be holding down for a long time - one for voice chat in game, another for voice chat on Discord/Teamspeak. The other two are for various things like telling OBS to start/stop recording, change scenes, etc.
The Makey-Makey board cost me ~$25, the buttons maybe $10, and the backplates were just crap I had laying around at work that was about to go in the dumpster.
If you're interested, I can message you a link to a google doc that has a simple build plan.
