What are you trying to accomplish? Are you looking to "just get by" or do you want to make it look like a factory double?

If you want to make it look like it came from the factory as a double you'll need a new crankset, bottom bracket and front and rear derailleurs. Your existing chain will probably be OK because you're only changing your big/big combination by 1 tooth.

If you replace the crankset you'll at least have to get a bottom bracket that's sized to work with a double. The derailleurs that you hav now will work but people will definitely notice so you'll lose style points.

The cheapskate way is to simply remove the granny chainring and dial in the low limit stop on your front derailleur. I don't see any benefit at all in doing that but at least the price is right. If you want to improve the chainline you can get yourself a shorter bottom bracket.