You will likely need a new front derailleur as well, to handle the larger difference between the front cranks. This would depend on the model of your existing front derailleur.

Depending on the cranks, you could keep the double and swap the chainrings to a smaller size. Moving from say, a 42/52 to a 34/48 would offer a much lower gear for climbing. Unfortunately this option is probably no cheaper than a larger capacity front derailleur.