Putting in a second floor includes tearing off the old roof. You can't just jack it up. Adding the second floor is like building a new house only one floor higher instead of ground level. Not only do you have the cost of building another house but add more cost go a floor higher, tear off old roof, fix everything torn up downstairs, redo the lawn and landscaping, then match old siding. Figure over $100,000 no matter where you live, 4 to 6 months to complete, and a whole new mortgage. Contact an architect and some contractors and go for it. It is your nickel after all but then again I would give the same advice whether you were bill gates or someone on welfare. It is doubtful the value of the house would be raised as much as was spent.
You'd be better off selling the house and buy one of the size that you need.
For Dr. whoever, it has been the common and worthwhile practice around here to give opinions and provide advice on whether to proceed with big and ill conceived projects such as putting in new kitchen cabinets inside a tar paper shack or to buy a house with a rotten foundation or painting a wrecked car without fixing the dents for that matter.