I'm an inch shorter than you and a little bit heavier. The harness I use on my FS250 appears to no longer be sold by Stihl but it resembles the current Universal Double Shoulder Harness (not the forestry harness) that's on their website. At first I didn't care for the asymmetric feeling of having padding around the left side of my torso with nothing to balance it on the right but I've since gotten used to it and it remains comfortable for extended use. If I was buying new right now, I would try and find the forestry model to try on. On the forestry model, I like how the connection point for the trimmer is around the center of your torso (front and back) like the included double harness that came with it. I should also point out that I never had a problem with the included double harness. I just wanted something better.
Also, the cheap orange trimmer line that comes with the Autocut head is grossly overpowered by the FS250. If you hit anything thicker than grass at full speed, it snaps off flush to the head and welds to itself on the spool. Throw it out and use Oregon Magnum Gatorline instead. The 0.095" square version works fantastic with the FS250. The triangle shaped 3-point brush blade is monster in heavier brush and should be on your short list of accessories to buy as well.
