Hi Deb,
The 900 x 1200 (or 1200 x 900) is the standard 4:3 aspect ratio for standard digital cams (including mine). That does explain why you are getting the "twiggy look" on shots. They are getting stretched vertical to fit the boxes. Yes, I know who Twiggy is....hehe
It's a tough question on whether it's better to not crop and use those striaght from the cam or crop to 3:2.
I would need to change the main image and thumbs for the 4:3 ratio. Not a problem. However, most clothing sellers are using 3:2, due it's elongation or bias to height vs. width. It does IMO work a little better for clothing ON A MODEL STANDING FOR PORTRAIT SHOT.
Cropping means every picture. There is cropping software that can always hit the 3:2 exactly, which can speed-up the process and make it exacting. Do you have any photo editing software with that cropping feature?
Your call on which you'd rather do.
Dan