a) a keyboard holder below the desk - something similar to https://kw.pricenacdn.com/files/images/products/original/14/... - I got mine from IKEA a long time ago - unfortunately they discontinued that product - the key thing here is the get the keyboard as close to your legs as possible, i.e. enabling your arms to be purely horizontally oriented while typing - or ideally even sort of downwards-pointing.
b) Microsoft Natural Keyboard Pro - manufactured 1999-2001 (e.g. https://mechanicalkeyboardtryout.blogspot.com/2016/03/micros... or http://www.dansdata.com/nkpro.htm) I have two of these; they're very durable. You'll need to wash the key caps in your dishwasher once a year.