[SVD]

There's a thread on here about a nifty set up for engraving - basically a highly adjustable work station that's wheelchair (or whatever chair) friendly.

Or, if it's just sitting that's the problem perhaps you could use a stand-up bench?

Then again with most bad back problems it's not sitting or standing - it's holding any position for too long. In that case I'd go with a stand up bench and a high chair - that would let you alternate between sitting and standing as appropriate / needed.