Many years ago my back would bother me if I was standing too long, sitting too long, lying too long, well... you get the picture. I tried EVERYthing and went to a number of medical professionals and naturopaths to try to find relief. There was nothing structurally wrong with my back and all attempts to "cure" me were useless. I thought I was doomed to a life of chronic back pain. One day, my Osteopath asked if I had ever considered acupuncture. I was skeptical, thinking that maybe it was something that you had to BELIEVE IN for it to work. He said that the treatment has been around for centuries and many people show significant improvement for a wide range of ailments, including back pain. I was willing to try anything, so I scheduled a visit.
On the first visit, the Acupuncturist spoke to me and explained how the treatment works. She told me that people "store" their life stress in different parts of their bodies... that some people get frequent headaches, some have chronic lower back pain, and who DOESN'T know someone who seems to have extremely tight and painful shoulder muscles? Anyhow... she began placing the tiny needles into my back at precise locations. I have to tell you I felt better than I had in a very long time after ONE treatment. I went back for more maybe eight or so more treatments over the next couple of months and have felt great ever since (that was over 10 years ago now). Sometimes I get temporary pain when I am moving furniture or working on some task on the floor for extended periods, but it is temporary.
Acupuncture might be something to consider. I swear by it and highly recommend it.
As far as your sink dilemma... I'm a little over 6'1" and, if I have a time consuming task at the kitchen counter, sometimes I spread my feet a little further apart to lower my trunk. I also try to multi-task where possible so I'm not stuck in one position, bent over, for extended periods of time.