I cannot believe that in the UK you are not able to find someone to recon your auto,with so many BMW cars there.Here in New Zealand i know of 5blokes i can go to and get the job done.i think you need to hunt a little harder !
Fitting up the 6speed is actually quite a big job in your car.Don't get me wrong...it can,and has been done.....lots of times.....down here anyway.........but it is a cost plus plus sort of job.You also need to buy a pedalbox to mount your clutch and brake pedals in,which is nothing but a curse to fit, ( the entire dash has to come out ) then you need a clutchfork and cables,speedo cable is different,driveshaft lenght is different,........makes the recon of the auto look easy ahy !!
Do you think your auto just needs a good flush out,new oil and pan screen ?
Hope this helps you. all the best.