Rear trailing arm front bush renewal

[keithcollins500]

Both bushes are warn, one side is split.
Is it a straight forward DIY job?
Is there a mild bush upgrade that is worthwhile and will it need the geometry recalibrated afterwards?
My M3 is '02 with 35k, is it common to fail so soon?
I live in Watford, any recommendations on where I could take it to be done professionally?
Lastly how long for a garage to do the job and what is the likely cost?
Thanks for the advice, cheers Keith