There are 2 "dive sites" in Houston...Twin Lakes which is south of downtown Houston near Pearland (about 20 minutes south of Downtown)
http://www.scubapark.net/
The other is in Huntsville about 1 to 1.5 hours north of Houston. It's called Blue Lagoon.
The website is not working now, but it likely will be back up again soon. It goes offline sometimes.
http://www.bluelagoonscuba.com
Of the two, Blue Lagoon is better than Twin Lakes in my opinion. Blue Lagoon is much clearer water and there are a few sunken boats and stuff to check out. Twin Lakes is pretty murky. The one thing Twin Lakes has going for it, is it has Fish. Blue Lagoon doesnt have any fish because the water is slightly Alkaline. It wont harm you, but it wont support algae which is why it's so clear, and why there's no fish.
Another alternative is to take a rig trip out of the Freeport area. I know Randy at Sport Divers has a boat. There are several charters though.
Randy is a member of SB, but I cant remember his name...I think it's CaptRandy?
http://www.sportdivers.com
You can just google for charters in the Texas Gulf Coast. I'd look for boats that run out of Freeport or maybe Galveston?
As for the 7mil? I'd say in November that should still be just fine......
Good luck, and hope you enjoy texas....