Replying to Ski size

Alright, since the forum search doesn't work, i have a ski size question to ask.
Im 5'3" 100 lbs, and im lookin at getting scratch pros for this year. I thought i would get 158s, but a guy at my local ski shop says that 148s would be better for me.
His argument is that since theyre wood core and pretty stiff compared to my old 1080 groms, (which are 145 cm foam core,so it seems to me that buying only 3 cm larger will be too small esp. if i want tow years) but he says the difference in flex makes up for the difference. Any thoughts?