And why does nobody seem to have a tire exactly like the one I'm replacing?

The size of my existing tire is 700 x 35, it's a rear tire, and the closest any bike shop near me has is 32 or 38. Based on the past threads I've read here, I'm tending toward the 38.

I'd appreciate any advice. The bike shop (who I've only talked to on the phone) said, "Um, yeah, that should work." Which sounded a little vague to me but maybe I'm overthinking this?

TIA!

Pam