Increase teeth on cassette from 11-32t to 11-34t 9 speed
One of the functions of a rear dérailleur is to take up the chain slack when the rider changes to the smaller gears.  The length of the derailleur limits how much slack it can take up, which puts a restriction on how big a gear can be on the rear cassette.  This review says that 32 teeth is as large a gear as a Sora rear derailleur can handle, but it's possible that things were different the year Shimano made your derailleur.

It might be possible for you to change your small chainring (in front) for a smaller one, but there are similar restrictions with the front derailleur: too small of a chainring will cause the chain to rub on the front derailleur cage.  Your LBS should be able to help you determine if you can change gear sizes, and can order the parts for you also.

I suspect that it won't be inexpensive or easy to put an easier gear ratio on your bike, and that the guy at the bike shop is right: training is the way to go.  Personally, I had lots of trouble with hills after I moved to a hilly area, but I decided to embrace the challenge and take them on, and I'm glad that I did; I'm much stronger now, and I have a lot more fun cycling.  Your mileage may vary of course.  Good luck!