Hah, well that is a bigger question than you may have imagined! 
I'll start by assuming that you want something that is otherwise a conventional keyboard. A quick Web search reminds me of the Keychron brand. Its offerings appear to be reasonably priced and well regarded.
To make sure you're looking at one of the programmable keyboards, Watch out for "QMK/VIA" in the product name or description. VIA is intended to be an easier way of programming keyboards than QMK (which looks daunting at first, but I would expect still gives more flexibility—I'm very used to it and happy with it).
The world of programmable keyboards is dominated by split keyboards. For instance, I use a Lily58, which is a split. I never got the hang of "normal" keyboards but touch typing on a split keyboard feels natural, improves ergonomics and involves no aches and pains! However, they take a lot of getting used to at first, as you would imagine!
To avoid your getting lost in a warren of very deep rabbit holes, I think I would suggest that a Keychron or equivalent conventional keyboard is likely get you off to a good start.
I hope that's a useful pointer. I think, from your posts, that you are someone who would gain enormous benefit from a programmable keyboard!