Well, I used to live in Houston but that was 23 years ago so I can't tell you where to stay now. But I can tell you that Houston is quite a ways from Galveston. Houston is a very very big city it takes hours to go from one end to the other.
However, the best hotels I have found for wheelchair access anywhere are the Staybridge Suites by Holiday Inn and the Homewood Suites by Hilton both have details added to their wheelchair accessible rooms that only someone in a wheelchair would have thought of. So if they have one of those chains near where you want to stay you can't go wrong with either one of them.