I have wrist problems also and what I discovered...and it really helps...is a suction handle thingy!! It is about 12" long and has a 3" suction cup at each end. What this does is distribute your weight over the ruler more evenly so the ruler doesn't tend to slip or slide. Quilt shops have them but they are also at Lowes, Home Depot or probably any hardware store sold as grab bars.
This site shows what they look like...
www.qualitymedicalinc.com