A good rule of thumb with handguns is use the largest caliber you can shoot accurately. My thoughts are that if you are not a gun enthusiast, then you probably should look at a medium size .38 Special revolver. It doesn’t have any fancy bells and whistles to get out of order, fires when the trigger is pulled, and hits hard enough to defend yourself with, although in my opinion it is marginal. I think also, if you are going to have only one gun between you and your wife, it makes a good compromise- you probably can handle a larger gun than your wife. All the same, I think having only one gun between the two of you is an error- his and hers do not have to be restricted to bathroom towels.
If you only want one firearm and do not want to start with a .22 I would recommend starting with a .38 Special revolver. Smith & Wesson or Ruger would be my first choices. They are simple but effective. You may later want to try a semiautomatic but the revolver is a good place to start.