A triple crank will most often require you to change the rear derailleur to a long cage, get a longer chain, a wider Bottom bracket spindle and a triple compatible front deraileur. if you have downtube shifters instead of STI levers they *should* be able to shift the new front derailleur through all 3 rings.

An alternative is a compact double with an overall lower range of gearing than a traditional racing double. I'm assuming you want to have a lower range of gears. what about your upper range? Are you really spinning out the 53x11 or 12t? How often are you actually in the 53? You can still retain the existing chain and derailleurs in most cases.

A compact double (110 bolt pattern, 48 or 50t outer ring, 34 or 36t inner ring) should give you a reasonable gear range. It will not be as high as a racing dbl, and not as low low as a triple.