No dog is 100% hypoallergenic, but I would recommend something like a Poodle, Maltese, or Shnauzer. Basenji's shed. Their fur is very fine, and it's not always easy to see, but it ends up everywhere.
A dog is not going to prepare you for becoming a parent. It's just not the same thing. Not even close. If you want a dog, research the breeds and try to figure out which would be best for you and your wife. If the dog is only a "test run" for your parenting skills, you will be better off becoming a "big brother/sister" or "foster parents". Even just the classes for these activities would open your eyes to what being a parent entails.
Most dogs are family/pack oriented. Which is great, if you have kids and bring home a puppy. Not so much if your dog is raised without children in the home and then suddenly kids appear.
Sit down with your wife and think it through together. Consider all of your options. And make the best choice you can with the information you have. Good luck.