Looks like you want a "compact" double, which would normally be 34/50 lowering your gearing a decent amount. Triple is another option, but that might require a new FD. Not sure how much you were looking to spend but here's a nice one for $60:
http://www.ebay.com/itm/SHIMANO-SORA...item35bb0bb131
Pretty surprised that now even Sora has gone to the external bearing setup. It's a 9 speed crank but should work ok with your current setup.
Originally Posted by
stowellt
Would need a new RD and chain to go to the 14-32 cassette, and would have a much wider ranger cassette making the gaps between gears bigger.
Replace the chainring? 53/39 = 130 BCD. Smallest ring that will fit is a 38T which will offer virtually no change in gearing.