If you wear glasses and want a full face, you need one of the Modular full face helmets. The whole front of the helmet flips up (not just the face shield). It looks like a 3/4 with a flipped up full face front.
I have one, bought it for $105 online. You put it on (with your glasses on) with the front flipped up. It's just like putting on a 3/4 helmet. Then when you're ready to ride pull the front down and it locks. Then it's a full face.
I love mine, has a flip up face shield also just like the normal full face helmets.
Mine is a Hawk. But you can get a modular in most any brand.
They have size charts online, and you measure the longest distance around your head above the ears at eyebrow level. Mine fit perfect, but most sites will let you exchange to the next size one time without a fee.
The problem with local shops is small selection and very high prices. Granted some helmets are better than others, but to get the same features I have on my Hawk was over $300 locally. As long as it has the DOT rating and you like it is all that matters.
If you're gonna wear a helmet might as well get all the protection you can out of it with a full face.