I developed tendonitis in my left wrist after having long practice sessions after a few consecutive days. I found that I was bending my wrist too much, which really was limiting the movement in my fingers in addition to causing pain in my wrist and forearm. I made things worse by pressing hard with the back of my thumb while fretting with my fingers. I found I had to raise my bass strap a bit (I like to play standing up), I had to pull my left elbow back while I was playing to straighten out the wrist while fretting, I started micro shifting more instead of trying to stretch my fingers a finger per fret low on the neck. This video helped me out a lot, I have seen it posted in other parts of this forum.
So for me, fretting with bent wrist is bad, squeezing neck with my thumb bad, bass too low bad, straight wrist good, bass higher on body good, light thumb on the back of the neck. Hope this helps.
And what @Vegaswizzle said, lower action is easier to fret, takes less finger strength