my ortho told me get those elbows at 90 degree angle--which for me meant getting a new sewing table that allows me to lower my machine and I use an office chair and raise it up a bit. I was still finding myself gradually lean over into the machine. DH bought a great memory foam pillow that has a lumbar "bump" and I was told to put it so I lean back. I also added a Big Look magnifying glass to that I can the needle better--I don't always use it but it does come in handy. And I have my ironing board on far side of the room so I have to get up and move.
thanks for the good exercise ideas, too!