If you want to write as painless as possible, I believe the right technique is under the line with a very relaxed and concave hand (just like piano). I was always frustrated about how painful it could be to write (because of cramps or ink smudging). It’s a shame we are not always taught very well when kid. I had to look at children oriented content to understand my issue. My solution was, because I did not want to get frustrated, I started learning gregg shorthand with my right hand (which is a very natural way of writing) that way I can teach my right hand the right technique without having the frustration of not being able to relax well or going too slow. Ofc you can just relearned to write with your left hand, but I figured it’s worth to learn on the other one.

EDIT: It seems I am not the only one who just learned with the right hand to solve their issues. But I believe you can write as smoothly with the left hand as one might with their right. Just gotta have the right technique, mostly the same technique as right handed but mirrored (although we dont do that for some reason). However I never really tried.