Shoring up the floor

[Chewy]

What would be a good method to add additional support to the floor in our place? 1951 pier and beam with wood floors. Not sagging or creaking or anything, but is noticably "soft" when several people or in the living room, or when we start jumping around with the kids. The answer I'm looking for is something that can be done over a weekend, if possible.

[Under_Miner]

Doubling up your floor joists and adding bridging and strapping is a great way to stiffen a floor and should only take a day or so, depending on how much your basement is finished.