The smallest I can go is a "65%" essentially the main keyboard area with an extra right column that generally houses pageup/down ins/del. The extra column allows for a full inverted t arrow cluster.

Something like this: https://d2rormqr1qwzpz.cloudfront.net/photos/2019/01/06/1059...

I've tried smaller boards, but as a software engineer having to do things like chord numbers or arrow keys is simply to much of a chore.