After some helpful comments from a few members on this site I decided to go ahead and fit a Bandit 12 (96-00) rear shock and I'm glad I did
.
The shock fits perfectly - the mechanic wasnt convinced it would work but after doing it he was well impressed and said it was a perfect fit and actually works very well!
The back end is now a LOT firmer, previously it was very soft but now it rides over large bumps a lot better and the bike is very composed through corners when 'making progress' where before it was wallowing and running wide.
The ride height of the bike has not changed at all - the shock is almost identical length to the stock shock and so hasnt changed the overall seat height at all.
Basically, the shock only cost me £20 from ebay and it has transformed the bike - there are lots of these shocks around on ebay so I would highly recommend fitting one if you are bouncing through corners at the moment as I was
. Only problem now is I need to sort the forks out too as the fimer shock has made me really notice the squidgy forks now!