Hardwood doors or double glazed doors?
 

I need a back door that doesnt shrink or swell in the weather. I know a double glazed one wouldnt do that but does a hardwood door not shrink or swell and could it withstand scratches from dogs paws? or would I better off with double glazed. Hardwood might be cheaper?

Order a fiber glass door with vinyl jams and brick moulding for a 100% maintaince free door. What I had to do with my door is install a piece of lexan (not plexaglass !) over the lower section held in place with stainles steel Oval head screws with finish washers under the heads to keep my dog from scratching up the door.
Any wooden door scratches, needs repainting or sealing, expands and contracts every time the moisture in the air changes.

This door company that I've worked with does a professional q&a about door issues. You could check it out if you're still looking. Nationwide Shipping Interior Doors, Exterior Doors From ETO California Door Company | Solid Mahogany, Solid Core Door, Custom Interior Doors

I would go with the double glazed

Double glazed means the door has two panes of glass in one hole and really has nothing to do with a doors, make up.
Google double glazing.

New Door
 

You could use doors and frames that are made out of materials such as, vinyl, aluminum and fiberglass.