I sit on whatever's available depending on which room I'm in. In my usual haunt, I sit on this high back wooden stool that I got from Ikea a decade ago. In the front room I sit on the sofa, in the kitchen one of the chairs there and in my bedroom, either the bed or the same high back stool. In the bathroom, I'll sit on the edge of the bath. If I'm playing double bass, congas, timbales or bongos {or singing}, I stand and if I play tablas or some of my little African or South American drums, I may kneel.
Apart from the conga/bongo/timbale position, all of the positions are more in the uncomfortable range, regardless of what I'd have to sit on although once I start recording I don't think about it so it doesn't get in the way although playing the double bass is pushing it sometimes. I mix on the high back stool which is not ideal in terms of comfort. Probably the one major advantage a computer and mouse would net over any other way of mixing would be that of comfort because then, I could sit in my computer chair which is really comfy. But I like the standalone way so it's an acceptable trade off while I just hope I don't succumb to scoliosis !
