Since I'm right here -- I'll jump on a reply.
I have an "office chair" and a shop stool - either one will saddle up nicely... no interference at all....
Welding depends on WHAT you're working on... normally though - I'm sitting on the office style chair if I'm TIG welding -- and standing when I'm MIG welding... I never MIG any small parts... only big ugly looking stuff
Welding is an "all position" proposition -- regardless of where when how and who...
You notice in one of my photos -- a copper strap? I use that sometimes under the ground clamp - and sometimes laying on a piece for holding and grounding -- and sometimes behind a hole I'm trying to fill (since welding won't stick to it).
In my "shed" I use a MAG clamp on my MIG and a spring loaded ground clamp on the TIG... I just snap either one on the table... I want my "machines" MOBILE... in a hot rod shop (shed) because you never know what you're going to be working on - or which of your buddies limps in with some broken "whatever".