Hey Mrs Nut! I'm new to this too. I just picked up a Marin Muirwoods 29er and I am in love with it. I'm 6'1" and 270. I looked at the Trek 7.3 and the 7.5 but with with the Muirwoods because of the feel (Very Solid) and the steel frame. It's considered and Urban/Hybrid. Not sure of your ht but they start at 17 in. Worth a check. Here is the link to Marin:
www.marinbikes.com
Good luck and keep us posted