I stand in my youth orchestra, but more and more I think I might try using a stool. I play my bass really high and its some times hard to play comfortable near the fingerboard. So my options are A) lower the bass, or B) play with a stool. To me the first option has lots of comfort draw backs; I would have to lean over more and have my intonation be changed until I could adjust. With I stool I think I would be able to reach all the notes about the same but I would be able to let the bass lean into me.
Another thought I had was, I wonder if orchestral players like the extra dampening from there leg on the bass. It seems like it would kill some of the extra ringing while playing loud and fast. Anyone know about this aspect of it?
If you lowered the bass you might try straightening your bow arm out a bit and letting it just hang. Try playing in front of a mirror and pay attention to your elbow, make sure it isn't raised.
How high exactly is your bass? I'm 5'6" but with long arms, and my bass has a 42" string length. When in playing position (I play with the bass fairly straight, but it leans into me a bit), first position A on the G string is in line with my eye-brow. This enables my bow to hang half way between the end of the fingerboard and the bridge. If you're finding that your shoulder is cramping from having the bass too high try examining if your left wrist is too bent while playing.