Your solution would not have met our local code, and my suggestion is to call your local building department, and simply pose the question to them. No need to give them your name, if you are planning to do it without a building permit. In our state the seller of any property worked on without obtaining a permit now is liable for damages at any time in the future should someone down the line have difficulty with any of the work done. Just some food for thought.
In a 1907 house I modified to change the attic to bedrooms I ended up having to triple each 2x6 floor joist. That means I used adhesive and nailed a 2x6 to each side of each of the original ceiling joists. I then applied 3/4" T&G subfloor in the normal manner and was left with a very solid floor. The key item in how you tackle it is the span of your joists. This is only a guess, but you might just get by with being able to double the joists instead of tripling them. Be sure to use adhesive and ringshank nails in the subfloor to avoid popping and squeaks.