Hector,
It took me a while to get use to sitting, and part of that was not hitting other strings. I do admit though, that mistakes still happen, and at times I do hit another string at the same time, but not very often. I find that when I play orchestral music, I prefer the bass to be more vertical, but when I'm playing solo like Bach or anything, I prefer it to be less vertical; but not so much that the neck is resting on my shoulder and I have to move to access the higher positions.
My 'technique checker' for sitting is:
1) Left leg should not be resting on the back of the bass because it will dampen it (Often I am the only bass player in the orchestra, so I need to be extra loud, so this is a big thing for me)
2) I need to be able to play anywhere on the board, at any time. That means that I need to be able to play the high harmonics, and reach half position all very easily with the least amount of movement.
3) Bowing needs to be easy. My right hand can't go too high to hit the G, or something in my posture is wrong.
4) At least one foot on the ground, the other on a rung.
5) I have to be able to page turn without getting up.
6) I still need to have a bit of movement available to me, and freedom (ala standing).
For me, that's the IDEAL when I sit. Sometimes I get uncomfortable because I practice a lot and my ass gets sore. But I don't even realize during a fun rehearsal or a good concert, so whatever.
Also, I find that when I do have random jazz gigs, sitting allows me to play jazz pizz a lot more varied. I can do triple stops and double stops, or things across the strings with my right hand a lot easier.
Herbie,
I spent a good deal of time, a while ago, finding a good sitting position with my bass, where my physical position in relation to the bass was very close to what it was while standing. I was pretty happy with my ability to move comfortably on the finger board, shifting and finding all the notes in tune, almost as comfortable and confident as when I was playing standing.
I had a terrible time adapting to the bowing position. I could bow well enough on any given string (easier on the lower strings though) but I had trouble finding the strings cleanly in across the string playing - string crossings were much more difficult.
Did you find any difficulty with bowing?