Go into your preferences and you'll see a styles list (it's the first item you'll see listed) - some have bigger fonts. Try Darker Full Width.
I've switched to darker full width and it just seems the same to me. If i go down to 150% zoom, then i'm almost at the point of needing my reading glasses, which i dont like to use when using computer.
13" is a small screen i have though, i had noticed when i got this Chromebook i was having to up the zoom level on every site i use. So its not really a big deal.