Honda Civic : vibration in cold start

I have a Nov 07 Honda Civic ( MT ) and am facing a peculiar issue since the past 4~5 months. The car vibrates a lot for the first 2~3 minutes when I start it in the morning and the RPM stays at ~1500. Once the engine temp increases, the vibrations go away and the car is very smooth and silent. I went to the AD and he advised Engine oil/oil filter/air filter/spark plug change which I have done. However, the engine vibrations have not gone away. The AD claims it is normal, but my friend's Civic doesn't have this issue in the morning. The yellow MI light also turns on intermittently which the dealer claimed is due to a faulty O2 sensor. He claimed the sensor is useless and only checks the pollution level. The estimated repair cost for this was 25K and he suggested not to get it done claiming this is a common issue in Honda engines. I checked on the net and found that O2 sensors are not that expensive if bought from outside. Can someone from TBhp please help me locate a dealer in mumbai/online where I can buy an O2 sensor from cheap and also where to get it installed ( Honda AD will not install spares bought from outside. They even refuse to let me purchase my own engine oil ) Apologies for the long post.

URL: