My sympathies for all with FM. My wife has it, and has since before they gave it a name. Back then, she was just told "It's all in your head," and "You'll never get any better." Sure made her day brighter.
Al1966 - I have a Mamiya Super Press 23 and love it. But there is weight to it. A wide strap helps, but weight is still there. Especially if you change to a 50mm or 250mm lens. The 65mm and 150mm aren't so bad, especially the 65. But if you can manage it, the photos are to cry for.
I mentioned folders before. I good one with a good lens might keep you out longer in the day. Weltas are nice, and I have a Zeiss 6x9 that although a little big (6x9 after all), is very light, and takes really good photos. Might be worth a try, if only for those times when you just really want to photograph, but can't afford weight.