Hi & Welcome Julie,
I also just returned to Houston after a long vacation (I see Kellie was gone too), so you're probably already in Texas.
Just in case you're reading this while still here...
My favorite quilt shop is Juliene's Quilt Shop in Old Town Spring, which is north of the airport and nestled among many charming little cottage shops. There really isn't much else quilty in Houston that I'd tell someone to specifically drive to during July, but there are a couple other nice shops that have been mentioned in this thread.
For non-quilty fun in Houston, consider visiting the Museum of Natural History where there is a way cool butterfly exhibit. It's a 3-story glass building with a rainforest atmosphere inside. Live butterflies hatch and fly about the plants and visitors on sunny days, so try to visit when it's sunny (no joke, we get daily afternoon storms this time of year).
Art doesn't get much better than in our little museum district (not too far from the one I just mentioned) so you won't be disappointed by a visit to the MFA Houston, the Contemporary Arts Museum (CAM) and there is also a craft museum, though I've not been there yet.